1. In a skillet, warm 1 tablespoon of olive oil over medium heat. Add the chopped onion and garlic and cook until softened. Stir in the chili powder and cumin, and cook for an additional minute. Add the diced sweet potato, quinoa, chopped tomatoes, and stock to the skillet. Bring to a simmer and cook for 10 minutes. Add the drained beans and continue to simmer for 20-30 minutes, or until the sweet potato and quinoa are tender and the sauce has thickened. Garnish with fresh cilantro and serve in bowls with a dollop of sour cream or yogurt, if desired.