Peel, core and cube apples into 1/4 inch dice. In a 12 inch to 14 inch saute pan, heat butter until foam subsides. Add onions and cook until soft and golden brown, about 8 to 10 minutes. Add apples and poppy seeds and cook until edges are softened, about 5 to 6 minutes. Add grappa and lower heat. Meanwhile, grill bread on both sides and place on platter. Place a cheese slice on each piece of bread. Spoon apples over and serve.