Pat the chicken breast dry with a paper towel and then cut into 1-2 cm slices, lengthways.
In a large bowl, whisk the egg and milk together with a fork.
Empty half the pouch of GF Kentucky-Style Coating Mix into a large bowl. Dip the chicken pieces in the egg & milk mixture one at a time, then press into the coating until fully covered on all sides. Place each coated chicken piece on a baking tray lined with baking paper and let sit for 20 minutes.
Prep burger fillings: Wash and dry lettuce leaves. Slice the tomato. Slice the gherkins and pickled onions, if not pre-sliced.
Time to cook the chicken. Place on a baking tray lined with greaseproof paper and bake in the oven at 180°C for 30-40 minutes. Alternatively, shallow fry in oil for around 3 minutes on each side, until golden and cooked through.
Once chicken is cooked, assemble your sandwich. Apply a generous amount of mayo and mustard to both sides of the bun and then layer your lettuce, tomato, chicken, pickled onion and gherkins.
Serve with a side of slaw or potato salad. Enjoy!