Place the rinsed buckwheat groats into a pan, cover generously with water, bring to the boil then simmer for around 15 mins until cooked. Drain the water and rinse under running cold water in a sieve until cool. If you are using pre-prepared buckwheat groats, you can skip this step.
While the buckwheat is simmering, place the banana, blueberries and yoghurt into a blender and whizz up until smooth.
Place all of the prepared ingredients into bowls and top with the nuts, seeds and mint leaves, if using. Serve.