Preheat the oven to 375°F (190°C). On a stable surface, lay out the chicken breasts and carefully slice a pocket along the side of each piece, being cautious not to cut all the way through.
In a small mixing bowl, combine the finely chopped spinach, diced roasted red peppers, shredded mozzarella, and the Italian seasoning. Mix thoroughly to evenly distribute the ingredients.
Divide the spinach mixture among the prepared chicken breasts, tucking the filling neatly inside each cavity. If necessary, secure the openings with toothpicks to prevent spillage during cooking.
Lightly coat the exterior of each stuffed chicken breast with olive oil. Sprinkle them evenly with salt, black pepper, garlic powder, and paprika for full coverage.
Place a large, oven-safe skillet over medium-high heat. Once hot, sear the stuffed chicken breasts for approximately 2 to 3 minutes per side, or until the surface is attractively browned.
Transfer the skillet directly into the preheated oven. Bake the chicken for 18 to 20 minutes, or until the internal temperature registers 165°F (74°C) at the thickest part.
Once removed from the oven, allow the chicken to rest for 5 minutes before cutting. Extract any toothpicks, then slice and serve while warm.