Wash each pumpkin; cut a 2-in. circle around stem. Remove top and discard. Remove loose fibers and seeds from the inside and discard or save seeds for roasting. Sprinkle insides of pumpkins with 1/2 teaspoon cinnamon. Place in a shallow roasting pan; add 1 in. of water to pan. Cover and bake at 350° for 45 minutes.
Meanwhile, in a large saucepan, combine the sugar, tapioca, salt and milk. Let stand for 5 minutes. Bring to a boil, stirring constantly. Remove from the heat. Stir a small amount of hot mixture into eggs; return all to the pan, stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer.
Remove from the heat. Stir in vanilla. Pour into pumpkins. Cover and bake 15-30 minutes longer or until pumpkins are tender. Sprinkle with roasted pumpkin seeds if desired and remaining cinnamon.