Preheat oven to 350 degrees F. Place uncut pumpkins in large shallow dish and add 1/4 inch of water; cover tightly with foil and bake for 40 minutes, or until tender. Let cool.
Reheat oven to 375 degrees F. With a paring knife, remove tops from pumpkins. Remove and discard seeds, then scoop out flesh, leaving 1/4-inch-thick shell.
Place four cups of pumpkin flesh in mixing bowl. Separate eggs, stirring yolks into pumpkin flesh and placing whites in separate bowl. Stir flour and baking powder into pumpkin mixture, then stir in cheese. Season with salt and pepper.
Whip egg whites into stiff peaks. Fold into pumpkin mixture. Spoon souffle mixture into pumpkin shells. Place on baking sheet and bake for 12-15 minutes, or until puffed and set.