01 - Preheat oven to 400°F. Lightly grease a baking dish with olive oil or cooking spray.
02 - Place chicken breasts on a cutting board. Carefully slice a pocket into the side of each breast, being careful not to cut all the way through.
03 - Season the chicken breasts with salt and pepper on both sides.
04 - In a mixing bowl, combine ricotta cheese, chopped spinach, 1/4 cup grated Parmesan, minced garlic, dried Italian herbs, nutmeg (if using), salt, and pepper until well blended.
05 - Fill each chicken breast pocket evenly with the spinach-ricotta mixture. Secure openings with toothpicks if necessary to hold the filling inside.
06 - Heat olive oil in a skillet over medium-high heat. Sear the stuffed chicken breasts for 2 minutes per side until lightly golden on the outside.
07 - Transfer the seared chicken breasts to the prepared baking dish. Top each breast with shredded mozzarella and the remaining 2 tablespoons of grated Parmesan.
08 - Bake for 20 to 25 minutes, or until the chicken is cooked through with an internal temperature of 165°F and the cheese is melted and bubbling.
09 - Remove toothpicks before serving. Let the chicken rest for 5 minutes, then serve hot.