Tortas, a type of Mexican sandwich, come in classic versions—and multiple variations on those classics—but they can be built any way you please. We make a hearty vegetarian version filled with sautéed mushrooms and chilies, refried beans, mashed avocado and cheese. You also could add lettuce, sliced tomatoes and cilantro. A flattish roll called telera is used for making tortas, but you can use any type of round roll with a soft interior and a thin, lightly crisp crust.