Open black bean cans, set aside, or cook dry beans using 6 cups water, 1 pound of beans and 1-3 teaspoons salt.
Simmer until very tender. Do not drain soak water.
In a large, heavy pan: e.g. skillet, dutch oven or electric frying pan, saute onion in olive oil until clear.
Add garlic and jalapeño sauce or peppers and saute.
Add tomatoes, lemon juice, beans and liquid, stir thoroughly. Simmer, mash and stir occasionally with a wooden spoon, until very thick (well-fried) approximately 30-60 minutes.
Serve on tortillas topped with cheese.