In a 12-inch skillet cook sausage and onion for 10 minutes or until sausage is browned and onion is tender. Drain off fat. Stir in undrained tomatoes, raisins, olives, tomato paste, vinegar, cumin, oregano, and crushed red pepper (if using). Bring to boiling; reduce heat. Simmer, uncovered, for 10 minutes or until sauce is thickened. Serve sausage mixture on toasted buns. Top with cheese and bun tops. Makes 6 sandwiches.