Increase heat to MEDIUM and add chicken, sausage, beans, tomatoes, Italian seasoning, paprika, salt, black pepper, and crushed red pepper (if using). Once mixture comes to a boil, reduce heat to LOW, cover the pot and simmer for 40 to 50 minutes, or until chicken is thoroughly cooked and fork tender. Stir spinach into hot stew and remove the pot from the heat. Allow the spinach to wilt from the heat of the stew and serve.