How to Make It
In a bowl, mash the avocado with a fork. Stir in the yogurt, lime juice, onion, jalapeño, cumin and 1 tablespoon of olive oil and season with salt and pepper.
In a large nonstick skillet, heat the remaining 2 tablespoons of olive oil. Add the chicken in an even layer and cook over moderately high heat until crisp on the bottom, about 3 minutes. Scatter the mozzarella and Cotija cheeses over the chicken, cover the skillet and remove from the heat. Let stand until the mozzarella is melted.
Split the rolls and spread the mashed avocado on the bottom halves. Top with the chicken mixture, then add the pickled jalapeños, tomatillo salsa and lettuce. Close the tortas and serve right away.