Top & core bell peppers and set aside. Brown ground beef in large sauce pan. Reduce to medium heat and mix in taco seasoning pkg. Add onions & cook for ten minutes until onions are opaque. Add undrained pinto beans and stir until thoroughly mixed. Remove from heat and stuff bell peppers with meat mixture leaving about 1 inch of space at the top. Top bell peppers with refried beans. Preheat oven to 350 degrees and cook uncovered for 45 minutes. Remove from oven and top with cheese of your choice. Continue cooking for an additional 10 minutes. Remove from oven, top with sour cream & and serve immediately.