01 - Preheat oven to 400°F. Lightly grease a baking dish with olive oil or nonstick 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 generously with salt and black pepper on both sides.
04 - In a mixing bowl, combine ricotta cheese, chopped spinach, 1/4 cup grated Parmesan cheese, minced garlic, dried Italian herbs, nutmeg (if using), salt, and black pepper. Mix until well blended.
05 - Fill each chicken breast pocket evenly with the spinach-ricotta mixture. Secure the openings with toothpicks if needed to keep 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 brown.
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 cheese.
08 - Bake for 20–25 minutes, or until the chicken is fully cooked through (internal temperature reaches 165°F) and the cheese is melted and bubbling.
09 - Remove toothpicks before serving. Let the chicken rest for 5 minutes, then serve hot.