Soak the black beans for about 8 hours (do not reuse the water that the beans were soaked in: it is full of starch, which is what makes the beans difficult to digest). Bring to a boil and simmer for 1½ hours or until the beans are tender; add more cooking water if needed.
Pour a little oil in a skillet and sauté 1 red onion, red pepper and black beans, adding cumin and garlic powder to taste. Pour in a little water, mix well and lower the heat to minimum.
Take each tortilla and place the cheese and black beans and vegetables on one half. Spread the other half with guacamole. Fold the tortilla over itself.
Serve with store-bought salsa, sour cream and cilantro, if desired.
