Put the buckwheat into a large saucepan of salted boiling water. Once the water comes back to boil, reduce the heat and simmer for 6-8 minutes. When done, it should still have a slight bite to them. Drain and leave to cool.
Mix the buckwheat, cucumber, tomatoes, radicchio, and pomegranate seeds in a bowl. Add the lemon zest and juice, three-quarters of the herbs and season with salt and pepper. Then gently toss everything together.
To serve, place the tabouleh in a large bowl, then pour over the olive oil. Scatter over the sumac and the rest of the herbs and drizzle over the pomegranate syrup.