Thanks for the reply! After having a look at the examples (and some others) this stuff is going way over my head. I usually find a way to solve things but they tend to be workarounds and probably the farthest from the correct way of going about it.
It's also a somewhat minor mechanic in the game and I'm not sure if it's worth my time (of which there is little) to try and learn how flood filling works.
My idea was to have a sprite (the same size as a tile of the tilemap) get spawned on the tilemap and have that sprite spawn 4 iterations of itself in each direction but only if there is a destructible tilemap underneath it. The sprite would then delete the tile that it collides with, and repeat. So, a hack based on collisions basically. But I guess it can't be done if I don't understand how to have an object collide with a specific tile on the tilemap.