1. Preheat oven to 325 degrees F. Mix apples with approximately 1 cup brown sugar, coating the apples, and spread mixture evenly in the bottom of a 10x13" cake pan.
2. In a bowl, add oats, flour, remaining brown sugar, baking powder and cinnamon. Stir together well.
3. Gradually add margarine and crumble with fingers until a chunky but not overly crumbly texture is reached (mixture should stick together when pressed firmly).
4. Place oat topping over the apples, and press together lightly. Put in oven, and bake for about 45 minutes, or until top is golden and apples are soft and fully cooked.
Serve warm with vegan vanilla ice cream. You can make more of the oat mixture if you prefer a thicker topping. There are endless fruit combinations possible, like pears, cranberries, strawberries, raspberries, peaches...