Heat oven to 400 degrees F. Grease 15-1/2 x 10-1/2 x 1-inch jelly-roll pan. Brush cut surfaces and inside of squash with tablespoon syrup. Arrange squash, cut side down, on pan.
Bake in 400 degree F oven for 30 to 40 minutes or until tender.
Meanwhile, toast walnuts in nonstick skillet over medium heat, stirring, 5 minutes or until golden and fragrant. Transfer to paper towel.
Heat oil in same skillet over medium-high heat. Add onion and celery; sauté 3 minutes, until just tender. Add apple, raisins, bulgur, broth, cinnamon and salt. Cover; simmer 15 minutes, until bulgur is tender and liquid absorbed. Stir in toasted walnuts.
Reduce oven to 375 degrees F. Turn squash, cut side up. Fill with apple mixture. Drizzle with remaining syrup. Bake in 375 degree F oven for 15 minutes. Makes 6 servings.