Vegan black bean brownies

Name: Vegan black bean brownies
Ingredients: 3tbsp coconut oil, plus extra for the tin; 80g dates; 80g walnuts, roughly chopped; 60g porridge oats; 400g can black beans, rinsed and drained; 1 very ripe banana, peeled and roughly chopped; 100g cocoa powder; 100ml maple syrup; 1tsp vanilla extract; 1tsp bicarbonate of soda; 2tsp baking powder; ¼tsp salt; 100g vegan chocolate chips; icing sugar, to serve