In a bowl, mix flour, sugar, baking powder, cinnamon, and salt. In another bowl, beat milk, pumpkin, egg yolks, and butter to blend. Stir into flour mixture until evenly moistened.
In another bowl, with a mixer on high speed, beat egg whites until soft peaks form. Gently fold egg whites into batter just until incorporated.
Place a nonstick griddle or a 12-inch nonstick frying pan over medium heat (350º); when hot, coat lightly with oil and wipe dry with a paper towel. Pour batter in 1/2-cup portions onto griddle, spreading slightly with the back of a spoon, and cook until pancakes are browned on the bottom and edges begin to look dry, about 3 minutes; turn with a wide spatula and brown other sides, 2 to 3 minutes longer. Adjust heat as needed to maintain an even temperature.
Serve pancakes as cooked, or keep warm in a single layer on baking sheets in a 200º oven up to 15 minutes.
Nutritional analysis per pancake.