Rinse the buckwheat groats in a sieve and transfer to a small pot. Add the water and the bouillon cube. Bring to a boil, cover, lower the heat, and simmer until the water has been absorbed, about 30 minutes.
In the meantime, preheat the oven by turning on the highest grill setting. Clean the mushrooms and remove the hard stems. Lay them in the ovenproof dish, rounded side down, and drizzle with olive oil. Grill for eight minutes, turning the mushrooms over after four minutes.
Chop the onion and garlic, and sauté in coconut oil in a skillet over low heat for about 2 minutes. Add the wine, cooked buckwheat groats, peas, oregano, pesto, and salt and pepper to taste. Stir to combine and continue cooking for another couple of minutes. Taste and adjust the seasoning if desired.
Position the mushrooms on a serving dish, top each with two tablespoons (30 g) of the buckwheat mixture, some grated goat’s cheese, a drizzle of olive oil, and a basil leaf.