Heat cast iron Dutch oven over high heat. Add oil and meat; cover and cook about 10 minutes. Uncover; boil down accumulated liquid. Meat will begin to brown, but not splatter. Brown well, stirring constantly. Add onions, seasoning and beer. Meanwhile, preheat oven to 325°. Reduce heat and cover. Bake 1 hour. Check during baking time to ensure that meat is covered with liquid (add water if necessary). Cook mushrooms in a little oil or butter 3 minutes only. Add lemon juice to mushrooms and stir into meat.