Preheat your oven to 375°F (190°C).

In a mixing bowl, combine the chopped spinach, cream cheese, mozzarella cheese, Parmesan cheese, minced garlic, Italian seasoning, salt, and black pepper. Mix until well combined.

Carefully slice a pocket into each chicken breast, making sure not to cut all the way through.

Stuff each chicken breast with the cheese and spinach mixture, using toothpicks to secure the opening if necessary.

In a large oven-safe skillet, heat the olive oil over medium-high heat. Once hot, add the stuffed chicken breasts and sear for about 3-4 minutes on each side until golden brown.

Drizzle the lemon juice over the chicken, then transfer the skillet to the preheated oven.

Bake for 20-25 minutes, or until the chicken is cooked through (internal temperature should reach 165°F).

Remove from the oven and let rest for 5 minutes before slicing and serving.