Process first 4 ingredients in a food processor until blended.
Cut squash lengthwise into quarters. Scoop out seeds and membrane. Spread half of butter mixture on squash. Bake, uncovered, at 400° for 30 minutes.
Stir together remaining butter mixture, orange juice, and vinegar in a small saucepan. Cook over low heat until butter melts; brush on squash. Bake 15 minutes or until squash is tender and golden, basting occasionally with butter mixture.