Add the chiles to an ungreased skillet. Cook over medium heat until lightly toasted, about 2 minutes, occasionally shaking the pan and turning the chiles as they cook. Remove from the heat. In a large mixing bowl, cover the chiles with simmering water. Place a lid or plate over the chiles to keep them from floating, and soak for 20 minutes.

Add the chiles and about 1/2 cup of the soaking liquid to a blender and puree, about 5 seconds. Scrape into a small bowl; set aside.

Meanwhile, in a large saucepan, heat the oil over medium heat. Add the onion, bell pepper, zucchini and garlic and cook, stirring, until tender, about 6 minutes. Stir in the remaining ingredients except for the tomato paste and the ancho puree and bring to a simmer. Reduce heat to medium-low and cook, stirring occasionally, until the potatoes are tender, about 20 minutes. Stir in the tomato paste and the chile puree and cook for 5 minutes.

Let the stew stand for 5-10 minutes before serving. Ladle into bowls and serve with flour tortillas.