01 - Preheat the oven to 400°F. Lightly grease a baking dish with olive oil.
02 - Pat chicken breasts dry and carefully cut a horizontal pocket into the thickest side of each without cutting through.
03 - Season the chicken inside and out with salt and freshly ground black pepper.
04 - Spoon 1 tablespoon of basil pesto into each pocket, then add mozzarella slices and chopped sun-dried tomatoes.
05 - Secure each stuffed breast with toothpicks if necessary to keep filling in place.
06 - Place stuffed breasts in the prepared baking dish, drizzle with olive oil, and sprinkle with grated Parmesan cheese.
07 - Bake for 25 to 30 minutes until chicken reaches an internal temperature of 165°F and cheese is melted and bubbly.
08 - Remove toothpicks, let the chicken rest for 5 minutes, then slice and serve.