01 - Preheat oven to 400°F. Lightly grease a baking dish large enough to hold the chicken breasts in a single layer.
02 - In a mixing bowl, combine ricotta, Parmesan, spinach, basil, garlic, nutmeg, salt, and pepper. Mix until thoroughly incorporated.
03 - Pat chicken breasts dry with paper towels. Using a sharp knife, carefully cut a horizontal pocket in the side of each breast without cutting through completely.
04 - Divide ricotta filling equally among the four chicken breasts. Fill each pocket and secure openings with toothpicks if necessary to prevent leaking.
05 - Brush the exterior of each breast with olive oil. Season evenly with salt and pepper on all sides.
06 - Place stuffed breasts in the prepared baking dish. Drizzle with remaining olive oil and sprinkle with Italian seasoning.
07 - Bake uncovered for 20 minutes until chicken begins to brown and filling is heated through.
08 - Remove from oven and top each breast with mozzarella cheese. Return to oven for 10 additional minutes until cheese melts and turns golden brown. Chicken should reach internal temperature of 165°F.
09 - Let chicken rest for 5 minutes before serving. Remove all toothpicks before plating.