Cook pasta per package directions, cooking only 7 minutes; drain. Spoon i nto a 13x9" baking dish. Cook and stir zucchini, red peppers, mushrooms, and scallions in hot olive oil in a skillet for 3-4 minutes. Add tomatoes. Spoo n over pasta. Whisk flour into drippings in skillet and whisk in milk, add broth, nutme g, and pepper. Cook and stir over medium heat until mixture thickens and comes to a boil. Add spinach and cheese. Pour sauce over vegetables & pasta. Cover with foil and bake at 350 degrees until thoroughly heated and chee se is melted.