Preheat the oven to 400°F and lightly oil a 9x13-inch baking dish.
Wilt the spinach in a large skillet over medium heat, 2-3 minutes. Let it cool slightly, then squeeze out the excess liquid and roughly chop.
In a bowl, mix the chopped spinach, feta, cream cheese and garlic with a pinch each of salt and pepper.
Pat the chicken dry and cut a deep pocket into the thick side of each breast, stopping before you cut all the way through.
Spoon one quarter of the filling into each pocket; press the opening closed and secure with toothpicks if needed.
Rub the chicken with olive oil and sprinkle with the paprika, remaining salt and pepper; arrange in the baking dish.
Bake 25 minutes, until the center of the filling reaches 165°F. Rest 5 minutes, remove toothpicks, and serve.
