1. Shape beef into six patties. In a large skillet, cook patties over medium-high heat for 5-7 minutes on each side or until a thermometer reads 160° and juices run clear. Remove to paper towels; drain, reserving 2 tablespoons drippings. Saute mushrooms in drippings until tender.
2. Meanwhile, in a microwave-safe bowl, combine soup and water. Cover and microwave on high for 2-1/2 to 3-1/2 minutes or until heated through.
3. Return patties to the skillet. Stir in soup mixture. Bring to a boil. Reduce heat; simmer, uncovered, for 3 minutes.
4. Top each patty with a slice of cheese. Remove from the heat; cover and let stand until cheese is melted. Serve on buns topped with mushrooms. Yield: 6 servings.