Cut each squash in half lengthwise; remove and discard seeds and membranes. Place squash halves, cut side down, in a 13- x 9-inch baking dish. Add water to depth of 1 inch.
Bake, covered, at 400° for 45 minutes. Drain. Return squash halves to dish, cut side up. Set aside.
Melt butter in a large skillet over medium heat; add onion, and cook, stirring occasionally, 20 minutes. Add pear and next 5 ingredients; cook, stirring occasionally, 5 minutes. Spoon mixture into squash halves.
Bake at 350° for 15 to 20 minutes.
Bring orange juice to boil in a small saucepan. Stir in sugar, and boil 10 minutes. Serve over squash.