Preheat oven to 220°C. Line a baking tray with baking paper. Place panko on prepared tray and bake for 5 minutes or until golden. Transfer to a shallow dish, then add parsley, stirring to combine.
Place egg in another shallow bowl and whisk in one tablespoon water. Place flour on a plate.
Working with one schnitzel at time, lightly coat chicken in flour, shaking off excess. Dip into egg mixture, then breadcrumb mixture, pressing to coat both sides. Transfer chicken to prepared tray and lightly spray with oil. Bake for 15 minutes or until golden and cooked through. Place rolls in oven for the last 3 minutes of cooking time to warm through, if desired.
Meanwhile, place cucumber and kaleslaw kit, including dressing, in a large bowl. Season with freshly ground black pepper, tossing well to combine. Place mayonnaise, juice and mustards in a small bowl, stirring to combine. Add a little water if mayonnaise is too thick.
Top roll bases with mustard mayonnaise, then schnitzel. Top with cucumber kaleslaw and serve sandwiched with roll tops.