01 - Preheat the oven to 400°F. Lightly grease a baking dish with cooking spray or oil.
02 - In a mixing bowl, combine the chopped spinach, softened cream cheese, shredded mozzarella, grated Parmesan, chopped sun-dried tomatoes, minced garlic, 1/4 teaspoon salt, and 1/4 teaspoon black pepper. Stir until all ingredients are evenly distributed.
03 - Using a sharp knife, carefully slice a deep pocket into the side of each chicken breast, ensuring you do not cut all the way through to the other side.
04 - Generously fill each chicken breast pocket with the spinach and cheese mixture. Secure the openings with toothpicks if needed to keep the filling enclosed.
05 - In a small bowl, combine the Italian seasoning, paprika, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Rub this seasoning blend evenly over all sides of each stuffed chicken breast.
06 - Heat 1 tablespoon of olive oil in a large ovenproof skillet over medium-high heat. Sear the stuffed chicken breasts for 2 to 3 minutes per side until a golden crust forms.
07 - Transfer the skillet directly to the preheated oven, or move the chicken to the prepared baking dish. Drizzle with the remaining 1 tablespoon of olive oil. Bake for 20 to 25 minutes, or until the internal temperature of the thickest part reaches 165°F.
08 - Remove the chicken from the oven and let it rest for 5 minutes. Remove any toothpicks before slicing and serving.