HEAT oven to 350°F.
CUT squash crosswise into 1-inch-thick slices; arrange in single layer in 15x10x1-inch pan. Melt 2 Tbsp. butter; brush onto squash slices. Cover. Bake 15 min.
CUT remaining butter into small pieces; place in medium bowl. Drain pineapple, reserving pineapple and juice separately. Add enough hot water to reserved pineapple juice to measure 1-1/2 cups. Add to pineapple mixture; stir until butter is melted. Add stuffing mix, pineapple, nuts, raisins, onions and pepper; stir just until moistened. Spoon evenly over squash slices.
BAKE 20 min. or until squash is tender and stuffing mixture is heated through.