Preheat oven to 375°.
Cook noodles in boiling water 5 minutes or until done. Drain and rinse with cold water; drain well.
Combine milk, 1/2 cup Swiss cheese, rosemary, and the next 5 ingredients (rosemary through cream cheese) in a blender or food processor, and process until smooth.
Heat oil in a large Dutch oven over medium heat. Add onion; cook 5 minutes or until tender, stirring frequently. Remove from heat; stir in noodles, cheese mixture, and spinach.
Place mixture in an 8-inch square baking dish coated with cooking spray; sprinkle with 1/2 cup Swiss cheese. Bake at 375° for 20 minutes or until bubbly and lightly browned.