
Invert squash in two ungreased 13-in. x 9-in. baking dishes. Add water and cover with foil. Bake at 375° for 40-45 minutes or until tender.
Meanwhile, cook the beef, celery and onion over medium heat until meat is no longer pink and vegetables are tender; drain. Add the apple, rice, sunflower kernels and curry. Cook and stir until apple is tender. Remove from the heat. Stir in the egg, 1 teaspoon brown sugar and 3/4 teaspoon salt.
Place squash cut side up on a baking sheet. Place 1 teaspoon remaining brown sugar and 1 teaspoon butter in each half. Sprinkle with remaining salt. Fill with meat mixture.
Bake, uncovered, at 375° for 15-20 minutes or until heated through.