Cook pasta according to package directions, omitting salt and fat. Drain.
Coat a nonstick skillet with cooking spray; place over medium-high heat until hot. Add onion and garlic; sauté 5 minutes. Add tomatoes, Worcestershire sauce, seasoning, and salt; bring to a boil. Reduce heat, and simmer, uncovered, 10 minutes. Stir in 1 cup cheese, cooked spaghetti, and chicken. Spoon into a 3-quart casserole coated with cooking spray. Sprinkle with remaining 1 cup cheese. Bake at 350º for 15 minutes.