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, opening like a book without cutting completely through. Season both sides with salt and pepper.
03 - Combine ricotta, chopped spinach, parmesan, mozzarella, garlic, nutmeg, salt, and pepper in a bowl. Mix until evenly distributed.
04 - Divide filling evenly among chicken breasts, spreading over one half. Fold opposite side over filling and secure with toothpicks if necessary.
05 - Place stuffed chicken in prepared baking dish. Brush tops with olive oil and sprinkle with remaining parmesan cheese.
06 - Bake for 25-30 minutes until internal temperature reaches 165°F and tops are golden brown.
07 - Remove from oven and let rest for 5 minutes. Remove toothpicks, slice crosswise, and serve immediately.