1. Combine the tomatoes, 1 cup of finely chopped onions, oregano, garlic, vinegar, sugar and salt for the sauce in a bowl and, with a large spoon, mix them together thoroughly. Set the sauce aside.
2. For the topping, prepare the frijoles refritos; cover them and keep them warm over the lowest possible heat. In a large bowl, beat the oil, vinegar and salt together until they are thoroughly combined.
3. Drop in the lettuce and toss lightly with a spoon until the lettuce is coated evenly with the dressing.
4. In a heavy 8- to 10-inch skillet, melt 2 tablespoons of the lard over moderate heat until a light haze forms above it. One at a time, fry the tortillas for 1 minute on each side, or until they are light gold.
5. Drain on a double thickness of paper towels. As you proceed, replenish the lard in the pan, 1 tablespoon at a time, when necessary.
ASSEMBLE:
1. Place 2 tortillas side by side on each serving plate.
2. Spread about 1/3 cup of the refried beans on the surface of each tortilla, scatter ¼ cup of lettuce on the beans, then top with layers of pig's feet, coarsely chopped onions and finally the sauce.
3. Sprinkle each "tostada" with 2 teaspoons of grated cheese and garnish with a few strips of "jalapeno" chili.
