Preheat the oven to 375°F (190°C).
Using a sharp knife, carefully cut a pocket into each chicken breast without cutting all the way through.
In a small bowl, combine the chopped spinach, roasted red peppers, mozzarella cheese, and Italian seasoning.
Divide the filling evenly among the chicken breasts and tuck it into each pocket. Secure with toothpicks if needed.
Rub the chicken with olive oil, then season with salt, black pepper, garlic powder, and paprika.
Heat a large oven-safe skillet over medium-high heat. Sear each side of the chicken for 2–3 minutes until golden.
Transfer the skillet to the oven and bake for 18–20 minutes, or until the Roasted Red Pepper Spinach Mozzarella Stuffed Chicken reaches an internal temperature of 165°F (74°C).
Rest the chicken for 5 minutes before removing the toothpicks. Slice and serve warm.