Preheat oven to 350 degrees.
Melt butter in a large skillet. Saute the onions and mushrooms in the butter. Add the green beans, mushroom soup, onions rings, and House seasoning to taste. Stir well.
Pour mixture into a greased 1.5-quart baking dish.
Bake for 20 minutes, then top the casserole with the cheddar and bake for 10 minutes longer, or until the casserole is hot and cheese is melted.