Take a bowl or glass and spoon the cold Greek yoghurt into it. Smooth the top with the back of a spoon so that a taut, flat base is created for the remaining ingredients.
Sprinkle the broken flaxseed into the bowl. Stir this through firmly and carefully with a spoon so that the flaxseed is completely and evenly incorporated into the yoghurt.
Break the walnuts by hand into coarse pieces. Sprinkle these walnut pieces over the yoghurt and then neatly arrange the fresh raspberries on top to finish.
Serve the dish immediately. By serving it right away, the yoghurt stays nicely cold and the fresh walnuts retain their firm and crispy texture.