Puree the tomatoes, onions, garlic, chipotle and adobo sauce in a food processor until completely smooth.
Heat the oil in a large Dutch oven or pot over medium-high heat until nearly smoking. Add the pork in a single layer, season with 1 teaspoon salt and 1/2 teaspoon pepper and cook, undisturbed, until beginning to brown, about 2 minutes. Turn the pieces and cook until brown, about 1 minute more. Dust the meat with the chili powder, and add the tomato puree, sweet potatoes, chicken broth, 1/4 teaspoon salt and a few grinds of pepper. Bring to a boil, reduce the heat to medium, cover and gently simmer until the meat is cooked through and the potatoes are tender, about 15 minutes.
Meanwhile, prepare the toppings: Chop the jalapenos, and whisk together with the yogurt in a small bowl. Shred the cabbage, cut the avocado into chunks and cut the lime into wedges.
Ladle the stew into large, deep bowls. Top with the yogurt mixture, garnish with the cabbage, avocado, lime and coriander and serve with the tortillas.
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