Preheat your oven: Begin by preheating your oven to 375°F (190°C). A warm oven ensures the chicken cooks evenly.
Prepare the filling: In a mixing bowl, combine the chopped spinach, ricotta cheese, mozzarella cheese, minced garlic, Italian seasoning, salt, and pepper. Stir well to incorporate all the flavors.
Prep the chicken: Take each chicken breast and make a pocket by slicing it horizontally without cutting all the way through.
Stuff the chicken: Spoon the filling mixture into each chicken breast pocket generously. Secure the openings with toothpicks to keep the filling inside while cooking.
Season and drizzle: Place the stuffed chicken breasts in a baking dish. Drizzle olive oil over the top and season with more salt and pepper if desired.
Bake: Bake in the preheated oven for 25-30 minutes or until the chicken reaches an internal temperature of 165°F (75°C).
Rest and slice: Once cooked, let the chicken rest for about 5 minutes before removing toothpicks and slicing.
Serve: Your stuffed chicken is now ready to enjoy!