Preheat oven to 200 F.

Cook the beans
In a large frying pan over medium high heat add the olive oil and cook the onion until soft. Add the cumin and cook for about 30 seconds, stirring constantly. This will bring up the flavor of the cumin. Add the beans, salt and water and using the back of a wooden spoon or a potato masher, mash the beans while stirring, until you get the desired consistency. Cook until the water is absorbed, then add the chipotle tabasco sauce, taste and adjust with more salt, if necessary. Remove from the heat, set aside and keep warm.

Prepare the tortillas
In a medium frying pan over medium high heat add half of the oil and wait until it heats up. To check if the oil is hot enough, dip the edge of a tortilla in. If bubbles start to form immediately, the il is ready.
Place a tortilla in the oil and cook it for 25 - 30 seconds on each side, until golden brown on both sides. Use a metal spatula to press the tortilla down while cooking to keep bubbles from forming. Grab the tortilla using tongs and allow excess oil to drip off of it back into the pan. Place the cooked tortilla on paper towels and sprinkle with salt. Repeat the procedure for all tortillas, placing cooked tortillas one on top of the other, with paper towels in between. Keep adding oil as needed and make sure you keep the oil temperature constant, at all times. Also, be carefull not to burn the tortillas; if they become too brown, lower the heat down a bit.

Assemble the tostadas
On a serving plate, lay a tortilla. Spoon over some of the refried beans mixture, top with the crubmled cheese and sprinkle with the chopped coriander. Serve with the tomatoes, iceberg lettuce, guacamole and sour cream.