Place the chicken breast halves in between plastic wrap and use a meat mallet or rolling pin to gently pound them until thin.
Place a skillet over medium-high heat and coat with oil. Add breadcrumbs to a shallow bowl. Add eggs to another shallow bowl and beat well.
Dip the chicken in the egg mixture on both sides, and then coat with breadcrumbs on both sides.
Place in the pan with the hot oil. Cook for a a few minutes on one side, until browned, then flip and cook on the other side until cooked through.
Slice the ciabatta rolls in half and toast them.
On the inside top half of the roll, spread a thin layer of mayonnaise, followed by a thin layer of refried beans and then a thin layer of mashed avocado.
Top the bottom half of the roll with cooked chicken, a few strings of mozzarella cheese, and a few pickled jalapeños.
Sandwich the roll together. Serve immediately.
*I make these easy semi-homemade refried beans or you can use canned refried beans. **In Mexico they use Oaxaca cheese, but since that is not as easy to find here, I use mozzarella string cheese, which is really similar in taste and appearance.***I love the La Costeña Brand of pickled jalapeños. Try them--they are not super spicy (in my opinion), but they add amazing flavor to the sandwich. They can be found in the Mexican aisle at any grocery store.