Using a sharp knife, cut a pocket in each pork chop. In a large skillet, sauté onion in butter until tender. Add spinach, cook until wilted. Stir in the stuffing mix, sour cream and sage.
Fill each chop with about 1/2 cup stuffing mixture; secure with toothpicks if necessary. Place on a greased 15-by-10-by-1-inch baking pan.
Sprinkle with lemon-pepper. Bake, uncovered, at 350 degrees for 35-40 minutes or until a meat thermometer reads 160 degrees. Discard toothpicks.