bool destroyAdjacentTiles(int x, int z) {
    int GridSize = Cubes.GetLength(0);
    int minX = x == 0 ? x : x-1;
    int maxX = x == GridSize - 1 ? x : x+1;
    int minZ = z == 0 ? z : z-1;
    int maxZ = z == GridSize - 1 ? z : z+1;
    
    Debug.Log(string.Format("Cube: {0}, {1}; X {2}-{3}; Z {4}-{5}", x, z, minX, maxX, minZ, maxZ));
    
    CubeBehavior thisCube = Cubes[x, z].GetComponent<CubeBehavior>();
    
    if (thisCube.isMine) { Destroy(thisCube); Cubes[x,z] = null; return false; } // TO DO: Make this = game over
            // BELOW: Always, no matter what, causes the object to destroy, dunno why. So I removed it for the time being.
    //if (thisCube.surroundingMines >= 1) Destroy(thisCube); return true;
    
            // if the function doesn't return by now, means it's a to-be-destroyed cube, so destroy it
    //Destroy(thisCube.gameObject);
    //Cubes[x,z] = null;

            //
    if (x > 0)
        if (Cubes[x-1,z]) destroyAdjacentTiles(x-1, z);
    if (z > 0)
        if (Cubes[x,z-1] != null) destroyAdjacentTiles(x, z-1);
    if (x < GridSize - 1)
        if (Cubes[x+1,z] != null) destroyAdjacentTiles(x+1, z);
    if (z < GridSize - 1)
        if (Cubes[x,z+1] != null) destroyAdjacentTiles(x, z+1);
    
    return true;
}

bool destroyAdjacentTiles(int x, int z) {
    int GridSize = Cubes.GetLength(0);
    int minX = x == 0 ? x : x-1;
    int maxX = x == GridSize - 1 ? x : x+1;
    int minZ = z == 0 ? z : z-1;
    int maxZ = z == GridSize - 1 ? z : z+1;
    
    Debug.Log(string.Format("Cube: {0}, {1}; X {2}-{3}; Z {4}-{5}", x, z, minX, maxX, minZ, maxZ));
    
    CubeBehavior thisCube = Cubes[x, z].GetComponent<CubeBehavior>();
    
    if (thisCube.isMine) { Destroy(thisCube); Cubes[x,z] = null; return false; } // TO DO: Make this = game over
            // BELOW: Always, no matter what, causes the object to destroy, dunno why. So I removed it for the time being.
    //if (thisCube.surroundingMines >= 1) Destroy(thisCube); return true;
    
            // if the function doesn't return by now, means it's a to-be-destroyed cube, so destroy it
    //Destroy(thisCube.gameObject);
    //Cubes[x,z] = null;

            //
    if (x > 0) {
        if (Cubes[x-1,z].gameObject) destroyAdjacentTiles(x-1, z);
        if (x < GridSize - 1)
            if (Cubes[x+1,z].gameObject) destroyAdjacentTiles(x+1, z);
    }
    if (z > 0) {
        if (Cubes[x,z-1].gameObject) destroyAdjacentTiles(x, z-1);
        if (z < GridSize - 1)
            if (Cubes[x,z+1].gameObject) destroyAdjacentTiles(x, z+1);
    }
    
    return true;
}

Update: I'm trying the recursive version of the Flood-fill algorithm, but I'm having trouble. In order to check the west adjacent tile, I use x-1, for the east, x+1 etc. Problem is, as soon as x = 0, it will infinitely loop between 0 and 1. I also have to check that that tile exists, so I'm using ifs to figure it out in order to not get an IndexOutOfRangeException (I tried using try/catch, but it's pretty much the same result, I figured this would be simpler). Here's my code right now (yes, I'm reproducing mineSweeper):

bool destroyAdjacentTiles(int x, int z) {
    int GridSize = Cubes.GetLength(0);
    int minX = x == 0 ? x : x-1;
    int maxX = x == GridSize - 1 ? x : x+1;
    int minZ = z == 0 ? z : z-1;
    int maxZ = z == GridSize - 1 ? z : z+1;
    
    Debug.Log(string.Format("Cube: {0}, {1}; X {2}-{3}; Z {4}-{5}", x, z, minX, maxX, minZ, maxZ));
    
    CubeBehavior thisCube = Cubes[x, z].GetComponent<CubeBehavior>();
    
    if (thisCube.isMine) { Destroy(thisCube); Cubes[x,z] = null; return false; } // TO DO: Make this = game over
            // BELOW: Always, no matter what, causes the object to destroy, dunno why. So I removed it for the time being.
    //if (thisCube.surroundingMines >= 1) Destroy(thisCube); return true;
    
            // if the function doesn't return by now, means it's a to-be-destroyed cube, so destroy it
    //Destroy(thisCube.gameObject);
    //Cubes[x,z] = null;

            //
    if (x > 0)
        if (Cubes[x-1,z]) destroyAdjacentTiles(x-1, z);
    if (z > 0)
        if (Cubes[x,z-1] != null) destroyAdjacentTiles(x, z-1);
    if (x < GridSize - 1)
        if (Cubes[x+1,z] != null) destroyAdjacentTiles(x+1, z);
    if (z < GridSize - 1)
        if (Cubes[x,z+1] != null) destroyAdjacentTiles(x, z+1);
    
    return true;
}

in my game I have a set of tiles placed in a 2D array marked by their Xs and Zs ([1,1],[1,2], etc).

Now, I want a sort of "Paint Bucket" mechanism: Selecting a tile will destroy all adjacent tiles until a condition stops it, let's say, if it hits an object with hasFlag.

Here's what I have so far, I'm sure it's pretty bad, it also freezes everything sometimes:

void destroyAdjacentTiles(int x, int z) {
    int GridSize = Cubes.GetLength(0);
    int minX = x == 0 ? x : x-1;
    int maxX = x == GridSize - 1 ? x : x+1;
    int minZ = z == 0 ? z : z-1;
    int maxZ = z == GridSize - 1 ? z : z+1;
    
    Debug.Log(string.Format("Cube: {0}, {1}; X {2}-{3}; Z {4}-{5}", x, z, minX, maxX, minZ, maxZ));
    
    for (int curX = minX; curX <= maxX; curX++) {
        for (int curZ = minZ; curZ <= maxZ; curZ++) {
            if (Cubes[curX, curZ] != Cubes[x, z]) {
                Debug.Log(string.Format("        Checking: {0}, {1}", curX, curZ));
                if (Cubes[curX,curZ] && Cubes[curX,curZ].GetComponent<CubeBehavior>().hasFlag) {
                    Destroy(Cubes[curX,curZ]);
                    destroyAdjacentTiles(curX, curZ);
                }
            }
        }
    }
}

In my game I have a set of tiles placed in a 2D array marked by their Xs and Zs ([1,1],[1,2], etc).

Now, I want a sort of "Paint Bucket" mechanism: Selecting a tile will destroy all adjacent tiles until a condition stops it, let's say, if it hits an object with hasFlag.

Here's what I have so far, I'm sure it's pretty bad, it also freezes everything sometimes:

void destroyAdjacentTiles(int x, int z) {
    int GridSize = Cubes.GetLength(0);
    int minX = x == 0 ? x : x-1;
    int maxX = x == GridSize - 1 ? x : x+1;
    int minZ = z == 0 ? z : z-1;
    int maxZ = z == GridSize - 1 ? z : z+1;
    
    Debug.Log(string.Format("Cube: {0}, {1}; X {2}-{3}; Z {4}-{5}", x, z, minX, maxX, minZ, maxZ));
    
    for (int curX = minX; curX <= maxX; curX++) {
        for (int curZ = minZ; curZ <= maxZ; curZ++) {
            if (Cubes[curX, curZ] != Cubes[x, z]) {
                Debug.Log(string.Format("        Checking: {0}, {1}", curX, curZ));
                if (Cubes[curX,curZ] && Cubes[curX,curZ].GetComponent<CubeBehavior>().hasFlag) {
                    Destroy(Cubes[curX,curZ]);
                    destroyAdjacentTiles(curX, curZ);
                }
            }
        }
    }
}