In a skillet, heat olive oil over medium heat. Add minced garlic and sauté for about 1 minute until fragrant.
Add the chopped spinach to the skillet and cook until wilted, about 2-3 minutes. Remove from heat and allow to cool slightly.
In a mixing bowl, combine the softened cream cheese, feta cheese, mozzarella cheese, sautéed spinach, onion powder, black pepper, and salt. Mix until all ingredients are well incorporated.
Using a sharp knife, create a pocket in each chicken breast by slicing horizontally along the side, ensuring not to cut all the way through.
Stuff each chicken breast with the spinach and cheese mixture. Secure the openings with toothpicks if needed.
Place the stuffed chicken breasts in a baking dish. Drizzle lemon juice over the tops of each breast.
Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and the internal temperature reaches 165°F (75°C).
Let the chicken rest for 5 minutes before removing toothpicks and slicing.
Notes
Serve with a side of roasted vegetables or a fresh salad.