Preheat oven to 350°F. Use a 2 1/2 quart casserole or baking dish. Coat it with cooking spray. Cook pasta according to package directions; drain.
Meanwhile heat oil in large non stick skillet (or Dutch oven) over med heat. Saute onion and garlic 3 minutes or until onion is tender, stirring frequently. Add milk and cream cheese to skillet; season. Continue cooking until cream cheese has melted, stirring frequently; do not boil (cream cheese does not need to melt completely).
Toss pasta and sauce together. Stir in cheddar cheese (reserve 2-tablespoons) and 2 tablespoons parmesan cheese. Pour into baking dish. Sprinkle with reserve 2 tablespoons each of cheddar and parmesan cheese. Bake uncovered for 20-25 minutes or until set. Let stand 5 minutes before serving.