Preheat oven to 350 degrees F. Lightly coat four 6-ounce ramekins or custard cups with cooking spray. Place ramekins in a 2-quart square baking dish; set aside. In a medium bowl stir together pumpkin, milk, the 1/3 cup brown sugar, the egg whites, and pumpkin pie spice. Divide pumpkin mixture among ramekins.
In a small bowl combine oats, the 1 tablespoon pumpkin seeds, the 2 teaspoons brown sugar, and the butter, stirring with a fork until crumbly. Sprinkle oat mixture evenly over pumpkin mixture.
Place baking dish on oven rack. Pour boiling water into the baking dish around ramekins to a depth of 1 inch. Bake, uncovered, for 40 to 45 minutes or until a knife inserted near the center of each pudding comes out clean. Carefully remove ramekins from water. Cool on a wire rack at least 15 minutes before serving. (Or, after cooling for up to 1 hour, cover and chill for up to 24 hours.) If desired, sprinkle with additional pumpkin seeds before serving.