Cut squash in half; discard seeds. Place squash cut side down in a 13x9-in. baking pan; add 1/2 in. of hot water. Cover and bake at 350° for 55-65 minutes or until squash is tender. Cool to room temperature.
Meanwhile, in a large bowl, combine the remaining ingredients. Remove squash from shell and add to bowl; mash until smooth. Transfer to an 8-in. square baking dish coated with cooking spray. Bake at 350° for 35-45 minutes or until heated through.