Heat 1 Tbsp. oil in deep large nonstick skillet on medium heat. Add onions and thyme; cook and stir 2 to 3 min. or until onions are softened. Add cream cheese product, Parmesan, cheddar, milk and reserved cooking water; cook and stir 2 to 3 min. or until cheeses are completely melted and sauce is well blended. Add pasta; mix lightly. Spoon into 9-inch square baking dish sprayed with cooking spray.