Preheat the oven to 350°. Heat olive oil over medium-high heat in a large oven-safe saucepan.
Add chicken and season with salt, pepper, paprika, garlic powder and half of the Italian seasoning. Brown on all sides approximately 5-7 minutes.
Add onion and garlic and saute until just beginning to soften, 3-4 minutes. Add cauliflower and season with additional salt and pepper.
Add the alfredo sauce, crushed tomatoes, diced tomatoes and remaining Italian seasoning. Season with another pinch of salt and pepper. Mix well and let simmer 5 minutes.
Add basil and spinach, stirring into the cauliflower mixture until fully wilted.
Add half of each of the cheeses and stir into the mixture. Sprinkle the remaining cheese over top of the casserole. Bake 12 minutes or until the cheese is melted. Switch the oven to broil and broil 2-3 minutes or until the cheese is golden brown.
Top with green onion. Let sit 10 minutes to thicken. Serve and enjoy.