Preheat oven to 350°. In large nonstick skillet, heat oil over medium heat and cook onion until soft and golden. Mix shredded sweet potatoes with sautéed onions and mustard. Mold mixture into separate cups in a muffin tin. Bake for 30 to 35 minutes or until crisp; cool in the pan. (This can be done a day ahead of time. Cover the cooled cups and wrap in plastic; refrigerate.) Scramble eggs with chicken, and when cooked, evenly divide among the sweet potato cups. Top with thyme and serve.