Heat the oil in a skillet over medium-high. Fry each tortilla flat for about 1 minute a side, until it stops bubbling and turns rigid and pale gold. Drain on paper and salt lightly.

To bake instead, brush both sides of each tortilla lightly with oil and bake at 400F for 10 to 12 minutes, turning once, until crisp.

Warm the drained beans in a pan with a splash of water, mashing them to a thick, spreadable paste. Season with some of the salt.

Warm the shredded chicken through in the same pan or a separate one, seasoning it with the rest of the salt.

{'Build each tostada in order': 'a layer of the bean paste spread to the edges, then the chicken, then the lettuce, tomato, avocado, queso fresco and a drizzle of sour cream.'}

Serve immediately, while the shell is still crisp.