In Mexico, these sandwiches would be made with telera or bolillo rolls (look for them in Mexican bakeries), but any large, crusty sandwich roll will be fine here.
1 lb. Yukon Gold potatoes, peeled and diced
5 oz. fresh Mexican chorizo, casings removed
1 can (15 oz.) pinto beans with liquid
1 tbsp. vegetable oil, plus more for brushing
4 telera or bolillo rolls
8 oz. Oaxaca cheese, shredded
1/4 Spanish onion, very thinly sliced
4 pickled jalapeños, sliced into strips
1 avocado, sliced
8 leaves Romaine lettuce
1 tomato, thinly sliced
1. In a small saucepan, combine potatoes with water to cover and season generously with salt. Bring to a boil and cook until just tender; drain and set aside.
2. Meanwhile, in a large skillet, cook chorizo over medium heat, breaking up large clumps and stirring, until browned, about 7 minutes. Add beans and oil and cook for 5 minutes, mashing gently with potato masher into chunky consistency.
3. Add drained potatoes to meat and beans mixture, reduce the heat and cook until liquid is mostly evaporated, about 5 minutes. Season with salt, set aside, and keep warm.
4. Preheat the broiler. Split rolls, brush lightly with oil, and broil, cut sides up, until light golden brown.
5. To assemble the sandwiches: On each bottom half, spread one-fourth of chorizo-potato mixture and top with cheese, onion, jalapeño, avocado, tomato, and lettuce. Top with other half of roll and cut in half.