replace blocks around an entity

So im new to datapacks and I'm trying to create a sort of "tornado" datapack where I spawn a tornado and it basically just does its own thing and damages blocks but I have encountered a roadblock. I don't know how to replace blocks around the entity (for now im using a cat as the tornado with the tags "tornado") and all I want pretty much is to replace any type of leaves and wooden blocks with gravel so If anyone can help me with that I would greatly appreciate it.