Cut the sweet potato into 5 or 6 pieces and drizzle with a little olive oil. Line a baking tray with baking paper and add the sweet potato to the tray. Bake at 200C/180C Fan/Gas 6 for 30 minutes or until soft to touch.
Line a square baking tin (8 inch by 8 inch) with baking paper and set aside.
While the sweet potato is cooking, make the oat flour. Put 100g porridge oats into a food processor and blend for up to one minute.
When the sweet potato is cooked, scoop out the soften potato from the skin and add to the oat flour in the food processor. Also add the maple syrup, peanut butter, vanilla extract and coconut oil. Blend for 30 seconds to combine all ingredients.
Add the cacao powder, sea salt and baking powder. Blend for another 30-40 seconds until all the ingredients are well mixed.
Transfer the brownie batter to the baking tin and spread out evenly. Top with the chopped pecans, 70% dark chocolate and chia seeds.
Bake for 30 minutes (at 200C/180C Fan/Gas 6) or until a toothpick inserted in the centre comes out clean. Cool in the tin for 30 minutes to one hour.