Preheat the oven 180 degrees F. Place the tortillas on a baking tray and bake them for 20 min or until they are hard & golden brown. Set aside.
Heat the oil in a saucepan to medium heat and add the onion, tomato, black garlic salt and pinch of cumin. Fry for 5 min.
Open the tin of beans and get rid of some of the liquid. Add the beans to the saucepan and cook until they start bubbling. Then turn the heat off and mash them with the potato masher. Set aside.
Crumble the feta cheese and slice the avocado. Then place some beans over a tostada. Scatter some feta, slices of avocado and your favourite spicy salsa! Place them on a platter and take them to the table to share with your family.