Cook spaghetti according to directions. Drain and set aside
In a large saucepan, over medium heat, cook bacon, onion, pepper, mushrooms until bacon is crisp. Add garlic last. Blend in flour. Add the undrained tomatoes, mushroom soup and milk. Stir and cook until mixture is thick and bubbly, then add cheddar cheese and stir until melted. Stir in spaghetti, chicken and peas. Salt and pepper to taste.
Pour mixture into a large casserole dish. Top with parmesan cheese. Bake, uncovered, for 45 minutes.