Put the buckwheat groats and quinoa in a medium bowl and cover with water. Soak for at least 5-6 hours, ideally overnight.
Preheat your oven to 360 F. Line a loaf tin with parchment...I recommend a loaf pan on the smaller size vs. a giant one.
Gently drain the soaked quinoa and buckwheat (you don't need to get all the liquid out, just do a quick drain through a mesh strainer).
Place in a food processor along with the oats, water, flax, pumpkin seeds, baking powder, apple cider vinegar, oil, and salt, and pulse to bring the mix together. I give it a good blend on low to medium for a few seconds at a time, but you want to keep a bit of texture. If it seems too dry you can add more water. You want a thick batter.
Pour the batter into your prepared loaf and sprinkle with whatever seeds (or salt) you've decided on.
Bake for between 65 and 80 minutes, until the sides have pulled away from the parchment and a skewer comes out clean. The time will depend on the size of your tin, but for me it's typically between 70-75 minutes.
Let cool for at least 10-15 minutes in the loaf pan, then remove from the tin and place on a wire rack to cool completely.