How to Make It
In a small pot, cover the sweet potato and yam with water and bring to a boil over high heat. Reduce the heat and simmer for 10 minutes, or until the vegetables are soft. Drain.
In a medium nonstick frying pan, heat the oil over medium high. Add the onion and cook for 2 minutes. Add the chopped chorizo and cook for 5 minutes, or until the chorizo cooks through. Add the garlic and Swiss chard leaves and cook for 1 minute, or until the Swiss chard starts to wilt. Add the sweet potatoes and yam to the pan and mix well. Season with sea salt and freshly ground pepper.
In a medium nonstick frying pan, warm the tortillas over medium high heat for 30 seconds each. Divide the sweet potato mixture evenly among the tortillas. Top with sour cream and roll into burritos.