In medium heavy skillet, melt 2/3 cup sugar over medium heat. DO NOT STIR, just shake occasionally. When starts to melt, reduce heat to low. Cook, stirring frequently, until golden brown. Quickly pour into 4, 6 oz. custard cups. Tilt to coat bottom.
Stir together eggs, pumpkin, milk, ¼ cup sugar, spice, orange peel, and vanilla. Pour into cups. Place in baking pan and place in oven. Pour boiling water in pan around cups to a depth of 1 inch.
Bake at 325 degrees for 40-45 minutes. Remove and cool. Chill 4 to 24 hours. Use knife to loosen edge of flan. Invert onto individual dish, scraping carmelized sugar onto the dish.