Cut squash in half; remove seeds and stringy fibers. Cut squash into 1-inch wedges. Arrange squash in 12 x 8 x 2-inch glass baking dish. Cover tightly with plastic wrap (do not vent). MICROWAVE (High) 5 minutes. Rearrange squash by moving outside pieces to center of dish. Cover tightly and MICROWAVE 4 minutes more. Drain squash and return to baking dish. Place butter in 4-cup glass measuring cup. MICROWAVE (High) 1 minute or until melted. Drain pineapple, reserving juice. Cut pineapple slices in half; set aside. Stir pineapple juice and brown sugar into butter. MICROWAVE (High) 2 minutes more. Add pineapple to squash and spoon brown sugar mixture over squash.