Preheat the oven to 375°F (190°C).
Place each chicken breast between two sheets of plastic wrap and gently pound with a meat mallet or rolling pin until about 1/4 inch thick.
In a medium bowl, combine chopped spinach, shredded mozzarella, grated Parmesan, and minced garlic.
Season both sides of each flattened chicken breast with salt, black pepper, and dried Italian seasoning.
Divide the spinach and cheese mixture evenly among the chicken breasts, spreading it over one side of each breast.
Carefully roll up each chicken breast tightly, starting from the edge with the filling, and secure with toothpicks.
Heat olive oil in an oven-safe skillet over medium heat.
Add the chicken roll ups and cook for 3-4 minutes on each side until golden brown.
Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
Remove the toothpicks before serving. Let the chicken rest for 5 minutes, then slice and serve.