01 - Preheat oven to 400°F. Lightly grease a baking dish large enough to hold chicken breasts in a single layer.
02 - Combine ricotta, Parmesan, spinach, basil, garlic, nutmeg, salt, and pepper in a bowl. Mix until thoroughly incorporated.
03 - Pat chicken breasts dry with paper towels. Using a sharp knife, cut a horizontal pocket in the side of each breast, taking care not to cut completely through.
04 - Divide ricotta mixture evenly among chicken pockets. Secure openings with toothpicks if necessary to prevent filling from escaping.
05 - Brush exterior of each breast with olive oil and season with salt and pepper. Arrange stuffed breasts in prepared baking dish. Drizzle with remaining olive oil and sprinkle with Italian seasoning.
06 - Bake uncovered for 20 minutes until chicken begins to brown and edges start to crisp.
07 - Remove from oven and top each breast with mozzarella cheese. Return to oven for 10 minutes until internal temperature reaches 165°F and cheese melts into a golden, bubbly topping.
08 - Allow chicken to rest for 5 minutes to retain juices. Remove toothpicks before plating.