Start by mixing together the shredded mozzarella cheese, chopped roasted red peppers, chopped basil, and red pepper flakes in a bowl. Set this mixture aside while you prepare the chicken.
Carefully slice a pocket into each chicken breast. Season both inside and outside with salt, black pepper, garlic powder, onion powder, and Italian seasoning.
Fill each pocket with the cheese mixture and secure with toothpicks.
In an oven-safe skillet, heat olive oil and sear each stuffed chicken breast for 2–3 minutes per side until golden brown.
Add minced garlic to the pan and cook until fragrant. Pour in chicken broth and balsamic vinegar, scraping up browned bits.
Transfer the skillet to a preheated oven at 375°F (190°C) and bake for 18–22 minutes until the internal temperature reaches 165°F (75°C).
Let the chicken rest for about five minutes before slicing. Serve with your favorite sides.