Preheat oven to 375°F (190°C).
Using a sharp knife, carefully slice a pocket into each chicken breast without cutting all the way through.
Season the chicken with salt, pepper, garlic powder, and Italian seasoning—both inside and out.
Stuff each chicken breast with spinach, roasted red pepper slices, and a slice of mozzarella cheese.
Secure the opening with toothpicks to keep the filling from spilling out.
Heat olive oil in a large oven-safe skillet over medium-high heat.
Sear the chicken breasts for 2-3 minutes per side until golden brown.
Transfer the skillet to the preheated oven and bake for 15–18 minutes or until the chicken is cooked through and juices run clear.
Let the chicken rest for a few minutes before serving. Don’t forget to remove the toothpicks!