In a large skillet brown the beef, green pepper and onion over medium heat until onions and peppers are soft and meat is no longer pink. Add water and taco seasoning and bring to a boil. Reduce heat and simmer for 5 minutes. stir in tomatoes and black beans (rinsed and drained). Simmer for 10 minutes.
Use a greased 9 x 13 pan. Put 2 tortillas on the bottom overlapping as necessary. Spread with half of the refried beans, then half of the meat mixture and 1 cup of cheese. Repeat layers starting with tortilla shells. Top with remaining tortilla shells and cheese. Cover with foil and bake for 30 minutes at 350 or until cheese is melted . Garnish with fresh cilantro if desired and top with sour cream.