I haven't finished anything, but I modified the code from https://github.com/danielmccluskey/A-Star-Pathfinding-Tutorial
I created a NavManager that attaches to the grid object. At start, it searches all the tilemaps for colliders. If the tilemap has a collider, it creates a wall node where it finds a tile. I choose to not go the same approach as the original scripts which does a bunch of raycasting and physics tests; though it seems like that was a mistake, as plants aren't included as a wall node. Easy to re-implement.
Secondly, I attached a NavAgent script to the player that gets a path from the NavManager. Using the path, I send the direction to the Mover script.
It works OK, needs more work. I was really surprised with how quickly I was able to get it working from the code mentioned above. Great scripts!