Preheat oven to 350 degrees.
Peel potatoes, cut in chunks. Bring to a boil in a pan of water; boil gently for 20 - 25 minutes until potatoes are fork tender.
While potatoes are cooking, brown hamburger and drain. Add salt, pepper, onion, and/or garlic while browning hamburger if desired.
Drain can of green beans and add to browned hamburger.
Add tomato soup to browned hamburger.
Stir and heat hamburger, beans, and soup for just a moment.
Mash potatoes with milk and butter.
Scoop hamburger mixture into a casserole pan.
Top with scoops of mashed potato.
Heat in oven until tips of mashed potato start to brown - about 20 - 25 minutes.