Preheat oven to 350°.
In a medium bowl, combine apple slices and cinnamon. Stir to combine. Carefully remove fillo dough packet from the box and unfold spreading sheets out on a clean counter. Take 1 single sheet, transfer onto another area of the flat counter and lightly coat with cooking spray. Lay another sheet on top and lightly coat with more cooking spray. Repeat until you have a total of 5 single sheets. With a sharp knife, cut fillo sheet into six squares. Coat a 2 oz. muffin pan with cooking spray. Press squares into prepared muffin cups. Fill center with apple filling and 1 teaspoon of walnuts. Top with raspberries and sprinkle with sugar (optional). Bake for 20-25 minutes.
Look for fillo dough that has no trans fat and no cholesterol and can be found in the frozen food aisle of the grocery store.
Raspberries get tart when cooked. Apples get sweeter when cooked.