01 - Preheat oven to 400°F. Lightly grease a baking dish large enough to hold chicken breasts in a single layer.
02 - In a mixing bowl, combine ricotta, Parmesan, spinach, basil, garlic, nutmeg, salt, and pepper. Mix until well incorporated.
03 - Pat chicken breasts dry with paper towels. Using a sharp knife, cut a horizontal pocket in the side of each breast, leaving edges intact to hold filling.
04 - Divide ricotta mixture evenly among chicken pockets. Secure openings with toothpicks if necessary to prevent filling from escaping during baking.
05 - Brush outside of each breast with olive oil. Season generously with salt and pepper on all sides.
06 - Place stuffed chicken breasts in prepared baking dish. Drizzle with remaining olive oil and sprinkle Italian seasoning over the top.
07 - Bake uncovered for 20 minutes. Remove from oven, top each breast with mozzarella cheese, and return to oven for 10 minutes until chicken reaches 165°F internally and cheese is melted and golden.
08 - Let chicken rest for 5 minutes to allow juices to redistribute. Remove toothpicks before plating.