Heat the oil in a large large pan over medium heat. Add the oil, onion, garlic, and jalapeño pepper. Cook for about 5 minutes, until the vegetables are soft.
Add the the beans, tomatoes, chili powder, salt, black pepper, and red pepper flakes to the pan. Cook for about 5 more minutes, until the mixture heated throughout.
Warm up your tortillas by placing them in a 250° oven for about 5 minutes while the bean mixture is cooking.
Lay the tortillas on 4 plates. Divide the bean mixture up and spread on top of the tortillas. Top each tostada with romaine, tomatoes, avocado, cashew cheese, and hot sauce, if using.