Combine sausage, onion, and green pepper in a large skillet; cook until sausage is browned, stirring to crumble meat. Drain well. Add tomatoes, macaroni, and sugar, stirring until well blended. Cover and simmer 20 minutes.
Remove from heat; stir in sour cream and 1/4 cup cheese. Spoon mixture into a 1 1/2-quart casserole. Sprinkle top with remaining cheese, and serve immediately.