Break spaghetti pieces in half. Cook according to package directions; drain (should have about 2-cups). In large saucepan, cook bacon, onion and garlic till bacon is crisp; blend in flour. Add undrained tomatoes, soup and milk. Cook and stir until thickened and bubbly. Add shredded American cheese, stir till melted. Stir in cooked spaghetti, cubed chicken, and thawed peas. turn into a 2.5-qt casserole; top with parmesan. Bake uncovered, at 180ºC or 45 minutes.