Pre-heat the oven to 350 degrees. In a large skillet melt butter and add mushrooms and garlic. Cook while stirring until mushrooms lose their moisture. Set aside.
Add green beans to a large saucepan and pour chicken broth over them. Bring to a boil and cook for 8-10 minutes or until green beans become fork tender. Drain green beans (but do not rinse).
In a large bowl combine cream of mushroom soup, cooked mushrooms, parmesan cheese, pepper, and onions rings, mix well.
Gently fold in green beans. Pour into a greased 3-quart casserole dish. Bake in the oven at 350 degrees for 20 minutes. Remove from the oven and sprinkle cheddar cheese over the top return to oven and bake for 5 minutes or until the cheese has melted.