Preheat the oven to 400°F (200°C).
Heat a skillet over medium heat and cook the chopped spinach for 2 to 3 minutes until wilted. Let it cool slightly and squeeze out any excess moisture.
In a mixing bowl, combine the spinach, cream cheese, mozzarella, Parmesan, minced garlic, parsley, and lemon juice until well blended.
Using a sharp knife, cut a deep pocket into the side of each chicken breast without cutting all the way through.
Stuff each chicken breast with the spinach mixture and secure the opening with toothpicks or kitchen twine.
Season both sides of the chicken with garlic powder, onion powder, Italian seasoning, paprika, salt, and black pepper.
Heat the olive oil in a large oven-safe skillet over medium-high heat.
Sear the stuffed chicken breasts for 3 to 4 minutes per side until golden brown.
Transfer the skillet to the oven and bake for 15 to 18 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
Remove the chicken from the oven and let it rest for 5 minutes.
Remove the toothpicks or twine before serving and enjoy warm.