Heat oil in a Dutch oven coated with cooking spray over medium-high heat. Add onion, bell pepper, and garlic; sauté 2 minutes. Add chicken; sauté 3 minutes. Stir in spaghetti sauce and next 6 ingredients (spaghetti sauce through mushrooms); bring to a boil. Cover, reduce heat, and simmer 25 minutes or until tender, stirring occasionally. Serve over pasta; sprinkle with cheese. Garnish with thyme, if desired.