you need to use sprites not the tilemap
I am sorry but that is not correct:
https://www.dropbox.com/s/bfwr6zs8mmzaf ... .capx?dl=1
Shoot at a cactus. Press the button to generate a new map when out of cacti to shoot. The collision polygon is a bit too small on them so it mail fail occasionally, that can be changed in the tilemap tools in the C2 editor.
That is one way to do it with just one tilemap, although for best performance I recommend using two tilemaps. One without collisions for most of the grapics and the other with collision for just the destroyable tiles. This is because only empty tiles do not have collision masks (it is not possible to disable collisions for specific tiles), therefore like in the example I linked to above, the "on collision" event will trigger every tick. If you would disable the second condition of the on collision event in my example which checks what tile the projectile collided with, the bullet would erase the tile on which the player is standing.
I use something similar for LOS with walls, walls are a separate tilemap from the surface and have collisions plus solid behaviour.