Prepare the Filling:
Preheat the oven to 375°F (190°C).
Heat 1-2 teaspoons of olive oil in a large skillet over medium heat. Add the spinach and garlic, cooking until wilted, about 3-4 minutes. Set aside and let cool slightly.
In a mixing bowl, combine the cream cheese, mozzarella, Parmesan, dried basil, dried oregano, onion powder, and red pepper flakes. Once combined, gently fold in the cooked spinach and sun-dried tomatoes. Set aside.
Prepare the Chicken:
Pat the chicken breasts dry with paper towels.
Use a sharp paring knife to create a pocket in each chicken breast, slicing along the side but being careful not to cut all the way through.
Stuff each chicken breast with the prepared filling. Sprinkle the tops of the chicken breasts with salt, pepper, and paprika.
Sear the Chicken:
Heat 1 tablespoon of oil (or the reserved oil from the sun-dried tomatoes) in a large oven-safe skillet over medium-high heat.
Once the oil is hot, sear the chicken breasts for 2-3 minutes per side, until golden brown. Work in batches if necessary.
Bake:
If your skillet is not oven-safe, transfer the seared chicken to a baking dish.
Bake the stuffed chicken at 375°F for 17-20 minutes, or until the internal temperature of the thickest part of the chicken reaches 165°F (74°C).
Allow the chicken to rest for 5 minutes before serving.
Serve with mashed potatoes and roasted green beans for a delicious, complete meal!