Preheat oven to 350°. In a saucepan, combine the squash, water, onion and salt. Bring to a boil. Reduce heat; cover and simmer until squash is tender, 15-20 minutes. Remove from the heat; cool., Stir in the egg, bread crumbs, butter and pepper. Transfer to a greased 1-qt. baking dish; sprinkle with cheese. Bake, uncovered, until heated through and the cheese is melted, 30 minutes.