Prep chicken: Pound chicken with a meat mallet until evenly thin. Add breadcrumbs and eggs to two separate shallow bowls. Dip chicken in beaten egg mixture, then coat in breadcrumbs.

Cook chicken: Place a skillet over medium-high heat and generously coat with oil. Add chicken and cook for a few minutes, flipping once, until crispy and cooked through.

Assemble: Toast ciabatta slices. Spread with a thin layer of mayonnaise, then refried beans and mashed avocado. Add chicken, a few strings of mozzarella cheese and a few pickled jalapeños. Serve immediately.