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, carefully cut a horizontal pocket in the side of each breast without cutting through completely.
04 - Divide ricotta filling evenly among chicken breasts. Stuff each pocket and secure openings with toothpicks if necessary.
05 - Brush exterior of each stuffed breast with olive oil. Season generously with salt and pepper.
06 - Place stuffed breasts in prepared baking dish. Drizzle with remaining olive oil and sprinkle with Italian seasoning.
07 - Bake uncovered for 20 minutes. Remove from oven, top each breast with mozzarella cheese, and return to oven for additional 10 minutes until internal temperature reaches 165°F and cheese is golden and bubbly.
08 - Allow chicken to rest for 5 minutes before serving. Remove toothpicks before plating.