In a large nonstick skillet, cook and stir ground beef until browned. Drain off excess fat.
Stir in salsa and water. Simmer for 10 minutes.
Meanwhile, cook pasta in boiling water until al dente. Drain.
Stir in green pepper and onions, and continue simmering until veggies are crisp/tender. Stir in noodles and sour cream. Sprinkle grated cheese on top, and cover pan until the cheese melts. Sprinkle chopped tomatoes on the top, and serve.