While buckwheat groats are simmering, heat oil in a large skillet over medium heat. Add shallots, celery, garlic, Brussels sprouts and saute until vegetables begin to soften and brown (about 5 minutes). Next, add fresh or dried thyme leaves, broth or water, salt and pepper to taste and simmer covered over medium low heat for about 10 minutes. Then add the Swiss chard, stirring to wilt for about 1 to 2 minutes. Lastly, add cooked buckwheat groats to the skillet, and stir to combine.