Cook and drain pasta as directed on package.
Meanwhile, in small bowl, stir 1/4 cup of the half-and-half, the flour, salt and nutmeg until smooth; set aside.
In 12-inch nonstick skillet, melt butter over medium-high heat. Add chicken; cook 6 to 8 minutes, stirring occasionally, until browned. Stir in tomatoes, mushrooms and spinach. Cook about 5 minutes, stirring occasionally, until mushrooms are tender.
Reduce heat to low. Stir in pasta and half-and-half mixture. Cook about 1 minute or until thickened. Stir in remaining 1 cup half-and-half. Sprinkle cheese over top. Cover; let stand 2 to 3 minutes or until cheese is melted.