Pour tomatoes into the bowl of a food processor, and pulse until coarsely ground (when it looks like jarred salsa, that's the right consistency.) Set aside.

In a large pot, heat vegetable oil over medium heat. When the oil is shimmering, saute onions for about 5 minutes. Stir in chili powder, cumin, and garlic, and cook for about 30 seconds, or until fragrant.

Pour in beans, chipotle chiles, and tomatoes. Simmer until slightly thickened, about 15 minutes. Stir in corn, and cook until heated through, approximately 2 minutes. If your chili is too thick, stir in water a few tablespoons at a time to desired consistency. Add salt and pepper to taste. Before serving, squeeze a lime wedge over each portion, and top with chopped avocado.