Preheat your oven to 375°F. In a large skillet, heat 1-2 teaspoons of oil over medium heat, and add the chopped spinach and minced garlic, cooking for 3-4 minutes until wilted. Remove from heat and let cool.

In a mixing bowl, combine the softened cream cheese, mozzarella, Parmesan, basil, oregano, onion powder, and red pepper flakes, then gently stir in the cooked spinach and garlic along with the sun-dried tomatoes. Set the filling aside.

Pat the chicken breasts dry with a paper towel. Carefully slice a pocket into the side of each chicken breast, taking care not to cut through to the other side. Fill each pocket with the prepared stuffing mixture.

Season the exterior of the stuffed chicken breasts with salt, pepper, and paprika. Heat the remaining olive oil in a large skillet over medium-high heat until glistening, then add two chicken breasts and sear each side for 2-3 minutes until golden brown.

If using a non-oven-safe skillet, transfer the seared chicken to a baking dish. Bake uncovered in the preheated oven for 17-20 minutes, or until the thickest part of the chicken reaches an internal temperature of 165°F. Allow the chicken to rest for 5 minutes before serving.