Thinly slice the cucumber and onion. Combine 1 tbs red wine vinegar and 1 tsp sugar in a large bowl. Add the cucumber and onion, season with salt and pepper and toss to coat. Set aside to pickle, tossing occasionally, until needed.
Step 2 — Prep ingredients
Finely chop the hazelnuts. Combine the hazelnuts and breadcrumbs in a shallow dish. Whisk 1 egg in a separate shallow dish. Combine 1 tbs flour and a pinch of salt in a third shallow dish.
Step 3 — Prep schnitzels
Preheat the air fryer to 200C (see cooking tip). Put the chicken flat on a board, put your hand on top and halve horizontally into fillets. Dust the chicken with the flour, shake off the excess, then dip in the egg and coat with the hazelnut breadcrumbs.
Step 4 — Air-fry schnitzels
Generously spray both sides of the chicken schnitzels with olive oil and put in the air-fryer basket. Air-fry the chicken, turning halfway, for 12-13 mins until golden and cooked through. Remove and keep warm.
Step 5 — Cook potato
While the chicken is cooking, cut the unpeeled potatoes into 2cm-thick slices. Put the potato in a medium saucepan of cold salted water and bring to the boil. Reduce the heat to medium and cook for 10 mins or until tender. Drain the potato and return to the pan. (Or cut the potatoes into 1cm-thick chips, toss in oil and air-fry for 18 mins.)
Step 6 — Get ready to serve
Add the aioli to the potato, season with salt and pepper and gently stir to coat. Drain the cucumber pickle. Pick the mint leaves, discarding the stems. Divide the chicken schnitzels, potato salad and cucumber pickle among plates. Scatter with the mint to serve.