Combine chia seeds and water in a small bowl and reserve.
In a big bowl, mix oats, buckwheat, coconut and hazelnut. Spread in a baking sheet and bake at 150ºC for 15 minutes, stiring from time to time. Remove from the oven and let cool.
In a small saucepan melt coconut oil, vanilla bean seeds and honey.
Blend the banana in a food processor with honey and oil mixture. Add in chia seeds (or egg white if using) and process just to combine.
Put the toasted oat mix in a big bowl with sultanas and spices if using. Pour in the liquid and stir well to combine.
Cover a baking pan (23*18cm aprox) with parchment paper. Spread mixture in the pan and press down firmly with a spatula so it get compact.
Bake for 25 minutes until golden. Remove from oven and let it cool.
Melt chocolate and drizzle over the cool granola tray. Let the chocolate set.
Cut in 10 slice or more if you prefer bite sizes. Store in a airtight container in the fridge.