Heat olive oil over medium high heat in non-stick skillet. Add chopped onion and minced garlic and sauté until translucent. Add ground chicken and cook to brown while using back of a wooden spoon to break up into smaller pieces – about 10 minutes.

Add sliced mushrooms, celery, red and yellow pepper, frozen green peas, Worcestershire sauce and dried oregano. Cook and stir another 5 minutes.

Make microwave white sauce by whisking milk and salt with cornstarch until dissolved. Microwave on HIGH power for 2 minutes, stir well and whisk in mustard powder, ground nutmeg and paprika. Microwave another 3 minutes on HIGH power. Remove and stir.

Spray a 3 quart (3 L) baking dish with vegetable oil spray. Puree canned tomatoes and mix with white sauce and pour into baking dish. Stir in the uncooked rice pasta and the chicken and vegetable mixture. Bake uncovered at 375°F (190°C) until pasta is tender; about 50 minutes. Stir half way through baking. Stir again when removed from oven and sprinkle with grated cheese. Let stand 5 minutes before serving.