01 - Preheat oven to 400°F. Lightly grease a baking dish with cooking spray or olive oil.
02 - Slice each chicken breast lengthwise through the thickest part, stopping before cutting completely through. Open like a book to create even thickness.
03 - Season both sides of each chicken breast with 1/2 teaspoon salt and 1/2 teaspoon black pepper, rubbing gently to adhere.
04 - Combine ricotta, chopped spinach, 1/3 cup parmesan, mozzarella, minced garlic, nutmeg, 1/4 teaspoon salt, and 1/4 teaspoon pepper in a bowl. Mix until evenly incorporated.
05 - Divide filling evenly among chicken breasts. Spread over one side of each breast, then fold opposite side over to enclose the filling completely.
06 - Secure stuffed breasts with toothpicks if needed. Place seam-side down in prepared baking dish, spacing evenly.
07 - Brush tops with 1 tablespoon olive oil and sprinkle with remaining 1/4 cup parmesan cheese.
08 - Bake for 25-30 minutes until internal temperature reaches 165°F and tops are golden brown.
09 - Remove from oven and let rest 5 minutes. Remove toothpicks, slice crosswise, and serve immediately.