Cook the buckwheat according to the packet instructions. Drain if necessary and set aside.
Finely chop the shallots and garlic.
Roughly chop the tomatoes, red pepper and shiitake mushrooms, cutting the mushrooms into smaller pieces if they are large.
Heat the olive oil in a large frying pan. Add the shallots and garlic and gently sauté for a few minutes until softened.
Add the red pepper, tomatoes and shiitake, followed by the chilli flakes, smoked paprika, oregano and cumin. Stir for about 1 minute to coat the vegetables in the spices.
Add a splash of the water and cook for about 5 minutes, stirring occasionally.
Add the remaining water and the drained cannellini beans.
Simmer until the liquid has reduced and the vegetables and beans are coated in a thick, savoury sauce.
Stir in the cooked buckwheat and chopped coriander. Season with salt and freshly ground black pepper to taste.
Serve hot, either on its own or with crumbled feta on top if desired.