Heat the oil in a skillet over moderately low heat. Add the onion and garlic and cook until softened. Add the garlic, cumin, and chili and cook for 1 more minute. Add the beans and 1/2 cup water, and cilantro cube, cover and simmer for 5 minutes. Mash the beans with the back of a fork and season with salt and pepper, to taste. Combine the chicken, 1/2 cup cheddar, chiles, and salt and pepper, to taste and toss well.
Warm the tortillas wrapped in a towel in a microwave for 3 minutes.
Spread 1/8 of the bean mixture on top of each tortilla, top with 1/8 of the chicken mixture and roll the tortillas up. Arrange them seam side down in a baking pan, top with remaining cheddar, and cover with foil. Bake for 15 to 20 minutes or until warmed through. Serve topped with sour cream and lettuce.