01 - Preheat oven to 400°F. Lightly grease a baking dish large enough to hold chicken breasts in a single layer.
02 - Mix ricotta, Parmesan, spinach, basil, garlic, nutmeg, salt, and pepper in a bowl until thoroughly combined.
03 - Pat chicken breasts dry. Using a sharp knife, cut a horizontal pocket in the side of each breast, being careful not to cut all the way through.
04 - Stuff each chicken breast with an equal amount of ricotta mixture. Secure with toothpicks if needed to prevent filling from escaping.
05 - Brush outside of each breast with olive oil and 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.
08 - Remove from oven, top each breast with mozzarella cheese, and return to oven for another 10 minutes until chicken reaches internal temperature of 165°F and cheese is golden and bubbly.
09 - Let rest for 5 minutes before serving. Remove toothpicks before plating.