Bring a small pot of water to a boil. Add chiles, tomato and bay leaf and turn heat down to a reallt slow simmer. Let simmer for 8 minutes.
While the chiles are simmering, heat a large pot to medium heat and add ¼ cup of water. Add onion and sweat until tender and translucent, about 4 minutes.
Add potatoes and sweet potatoes and 1 cup of vegetable stock. Cover and let simmer for about 6 min or until potatoes are beginning to become tender, but are not fully cooked.
Strain the chiles, but reserve one cup of the chile soaking liquid. Place the drained chiles, garlic, tomato, oregano, cumin, and 1 cup of the chile soaking liquid in the blender and blend until smooth. Strain the sauce.
Add sauce, chickpeas, and sprigs of thyme to the pot. Let simmer slowly for 8-10 minutes or until the sweet potatoes are cooked through. If the sauce is too thick, add more vegetable stock accordingly.
Season with salt and pepper. Remove thyme sprigs before serving.
Serve with rice and warm corn tortillas.
Instead of sweet potatoes you could use russet, yukon gold or any other type of potato. The chickpeas could be substituted with any other bean. Cauliflower or tofu would also be a great addition to this dish.