Pre-heat your oven to 400°F. Place the cream cheese, mozzarella, and spinach in a microwave safe bowl. Heat for about 2 minutes, or until the cheeses get melty and can be easily mixed together. Mix the filling and add salt and pepper to taste.
Cut several horizontal slices across each chicken breast, Cut as deeply as you can without slicing all the way through the chicken.
Season the chicken with salt and pepper.
Stuff each piece of chicken with the cheese filling.
Brush some olive oil onto the bare chicken tops. Cook for 25 minutes, or until chicken reaches 165°F.
Change your oven to the broil setting. Top with Rao's tomato sauce, and the slices of mozzarella.
Broil for 5 minutes, or until the cheese gets melty and starts to brown.