Line a baking sheet with foil; lightly grease the foil. Set baking sheet aside. For filling, in a medium bowl stir together spinach, cream cheese, green onion, Parmesan cheese, and black pepper. Set aside.
Unroll pizza dough on a lightly floured surface; roll dough into a 15-inch square. Cut into twenty-five 3-inch squares. Spoon 1 rounded teaspoon filling onto each square. Brush edges of dough with water. Lift a corner of each square and stretch dough over filling to opposite corner, making a triangle. Press edges with fingers or a fork to seal.
Arrange the pockets on the prepared baking sheet. Prick tops of pockets with a fork. Brush with milk. Bake in a 425 degree F oven for 8 to 10 minutes or until golden brown. Let stand for 5 minutes before serving. If desired, serve with spaghetti sauce. Makes 25 pockets.