Cook pasta according to package directions, omitting salt and fat. Drain in a colander over a bowl, reserving 1/4 cup cooking liquid.
While pasta cooks, heat a large nonstick skillet coated with cooking spray over medium-high heat. Add onion; sauté 2 minutes. Add basil, garlic, and crushed red pepper; sauté 1 minute. Combine half-and-half, sour cream, and flour, stirring with a whisk. Add reserved pasta cooking liquid and half-and-half mixture to pan; bring to a boil. Stir in salt, black pepper, chicken, and spinach; bring to a boil. Stir in pasta, and cook 1 for minute or until thoroughly heated. Sprinkle with cheese.