Boil your green beans for about ten minutes until cooked through. Drain. Set aside.
In a medium saucepan over low heat sauté diced onions, thyme, parsley, and garlic in butter for 5 minutes.
Blend in salt, pepper, flour and lemon peel. Add sour cream and sherry, and cook on low for 3 minutes.
Grease a medium/large casserole dish with butter, add cooked and drained beans along with sliced mushrooms to the dish. Pour the sour cream and spice mix over the beans, stir gently to coat. Sprinkle shredded cheese over the top.
Bake at 350 degrees for 20 minutes. Remove and top with friend onions. I like to cover the top completely with fried onions. Then bake another 10 mins until golden. Then serve and enjoy!