Make a small cut into each squash; microwave at HIGH 1 to 2 minutes to ease halving squash. Cut squash in half crosswise; remove and discard seeds. Place squash, cut side up, in a 13" x 9" x 2" baking dish.
Combine pear, brown sugar, ginger, butter, and, if desired, liqueur; spoon evenly into squash halves. Add boiling water to a depth of 1/2" to dish. Cover and bake at 350° for 1 hour and 15 minutes or until squash is tender. Transfer squash to a serving dish; sprinkle with toasted hazelnuts.
*To remove hazelnut skins, cook hazelnuts with 1 teaspoon baking soda in boiling water 30 to 45 seconds. Drain nuts; rub with dish towel (skins come right off). Dry before toasting.