Preheat oven to 375*F. Spray 2-1/2 quart casserole/baking dish with nonstick cooking spray. Cook pasta according to package directions; drain.
Meanwhile, heat oil in large nonstick skillet (or Dutch oven) over medium heat; sauté onion and garlic 3 minutes or until onion is tender, stirring frequently. Add milk and cream cheese to skillet; season with salt and pepper. 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 reserved 2 tablespoons each Cheddar and Parmesan.
Bake uncovered at 375*F 20 to 25 minutes or until set. Let stand 5 minutes before serving.