Preheat oven to 400º. Line two baking sheets with parchment and set aside.
Beat egg and water together in a small bowl; set aside.
Stir Muenster, Parmesan, and garlic powder together. Set aside.
Lightly flour work surface. Unfold the thawed puff pastry and roll lightly with a floured rolling pin. Brush the surface with the beaten egg. Top with cheese mixture, then evenly top with thawed spinach.
Starting at the short end, roll up like a jelly roll. Slice at ½-inch intervals and place rounds on baking sheets. Brush with egg wash.
Bake for 15 minutes or till golden brown. Remove to wire racks and let cool for 10 minutes before serving.
