In 12-inch nonstick skillet, heat 1 tablespoon of the oil over medium-high heat. Add sausage, onions and garlic; cook and stir 5 to 7 minutes or until sausage is no longer pink. Reduce heat to medium; add flour, salt, pepper, pepper flakes and nutmeg. Cook and stir 1 minute. Gradually add spinach. Cook and stir just until spinach is wilted. Stir in whipping cream. Heat to boiling; cook and stir 1 to 2 minutes or just until thickened. Remove from heat; stir in mozzarella and 1/2 cup of the Parmesan cheese until melted.