Preheat the oven to 180°C top/bottom heat.
Dice the pumpkin (without seeds) and cook in 60-80mL water for 5-10 minutes until the liquid has completely evaporated.
Set aside to cool, then puree with the oat drink.
In a mixing bowl, mix flour, starch, sugar, baking powder, vanilla, and salt. Add the oil, soda, and vinegar, then mix the pumpkin mixture and hand whisk into a smooth batter.
Line a 20x20cm square loaf tin with baking paper and pour in the dough.
Peel and core the apples, then cut them into thirds and score. Place the apple thirds in the batter.
In a small bowl of flour, sugar, margarine, and cinnamon, mix the crumble and sprinkle over the cake.
Bake for 45 minutes until golden, then allow it to cool in the tin.
Serve with powdered sugar and some maple syrup.