Brown ground meat in a skillet over medium heat. Season meat with salt and pepper. Stir occassionally to break up the meat. When the meat is no longer brown add the can of drained mushrooms to the skillet.
Add green beans, 1/2 onion rings, mushroom soup, and mix. Put into a casserole dish top with remaining onion rings. Bake for about 30 to 35 minutes
I have also made this green bean casserole with frozen green beans with good results. There is also a mix of frozen vegetables called Oriental mix that contains, mushrooms, onions, and broccoli that this casserole works well with too. Use you imagination on this one!