In a small pot, bring the vinegar, water, salt and sugar to a boil.
Add the vegetables to a large jar, pack them tightly into the bottom of the jar, and add the hot vinegar/water mix into the jar
Place the lid on tightly, let the jar cool, and leave in the fridge overnight*
For the tostadas
Blend the beans, sauce, water, and cumin into a consistent paste
Spread it onto the tostadas, and top with the pickled vegetables (see below) and avocado. Enjoy!
Recipe Notes
The longer you leave the pickled vegetables in the fridge, the more the flavors will develop. Store any leftover pickled vegetables in the jar, in the fridge.