01 - Preheat oven to 400°F. Lightly grease a baking dish with cooking spray or oil.
02 - Slice each chicken breast lengthwise through the thickest part, opening like a book without cutting completely through.
03 - Season both sides of each chicken breast with 1/2 teaspoon salt and 1/2 teaspoon black pepper.
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 well blended.
05 - Divide spinach ricotta mixture evenly among chicken breasts, spreading over one side. Fold opposite side over to enclose the filling completely.
06 - Secure with toothpicks if needed and place stuffed breasts in the prepared baking dish, seam side down.
07 - Brush tops with 1 tablespoon olive oil and sprinkle with remaining 1/4 cup parmesan cheese.
08 - Bake for 25-30 minutes until chicken reaches internal temperature of 165°F and tops are golden brown.
09 - Remove from oven and let rest for 5 minutes. Remove toothpicks, slice crosswise, and serve immediately.