01 - Preheat your oven to 400°F (200°C). Lightly grease a baking dish with cooking spray or a small amount of oil.
02 - Butterfly each chicken breast by slicing lengthwise through the thickest part, being careful not to cut all the way through. Open the breast like a book to create two even halves that remain connected.
03 - Season both sides of the butterflied chicken breasts evenly with 1/2 teaspoon salt and 1/2 teaspoon black pepper, pressing gently to adhere.
04 - In a medium bowl, combine ricotta cheese, chopped spinach, 1/3 cup grated parmesan, shredded mozzarella, minced garlic, nutmeg, 1/4 teaspoon salt, and 1/4 teaspoon black pepper. Mix until thoroughly incorporated.
05 - Divide the spinach ricotta mixture evenly among the 4 chicken breasts, spreading it over one half of each butterflied breast. Fold the other side over to enclose the filling completely.
06 - Secure the chicken breasts with toothpicks along the edges if needed to prevent filling from escaping. Place them in the prepared baking dish, seam side down.
07 - Brush the tops of each stuffed chicken breast with 1 tablespoon olive oil and sprinkle evenly with the remaining 1/4 cup grated parmesan cheese.
08 - Bake for 25-30 minutes, or until the chicken is cooked through (internal temperature reaches 165°F/74°C) and the tops are golden brown and crispy.
09 - Remove from oven and let the chicken rest for 5 minutes. Remove toothpicks carefully, slice crosswise to display the filling, and serve immediately.