Preheat the oven to 375°F (190°C).
In a mixing bowl, combine chopped spinach, artichoke hearts, cream cheese, mozzarella cheese, Parmesan cheese, minced garlic, Italian seasoning, salt, and pepper.
Slice a pocket into each chicken breast, being careful not to cut all the way through.
Stuff each chicken breast with the spinach artichoke mixture, securing the openings with toothpicks if necessary.
Heat olive oil in a skillet over medium-high heat. Sear the stuffed chicken breasts for 3-4 minutes on each side, until golden brown.
Transfer the chicken to a baking dish and bake for 25-30 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
Let the chicken rest for 5 minutes before slicing and serving.