Preheat the oven to 220C, fan-forced. Line an oven tray with baking paper. Cut the unpeeled potatoes into thin wedges and put on the lined tray. Drizzle with 2 tsp olive oil, season with salt and pepper and toss to coat. Roast, turning halfway, for 25 mins or until golden and tender.
Step 2 — Prep ingredients
While the wedges are roasting, peel the cucumber into ribbons with a vegetable peeler. Thinly slice the onion and tomato.
Step 3 — Pickle cucumber
Put 1 tbs white wine vinegar, 1 tsp sugar and 1 tsp wholegrain mustard in a bowl, season with salt and pepper and stir to dissolve the sugar. Add the cucumber and toss to coat. Set aside to pickle, tossing occasionally, until needed.
Step 4 — Cook onion
Heat 2 tsp olive oil in a medium frypan over medium heat. Cook the onion, stirring regularly, for 6-7 mins until golden. Remove from the pan and keep warm. Reserve the pan.
Step 5 — Prep and cook chicken
Meanwhile, put the chicken flat on a board, put your hand on top and halve horizontally into fillets. Scatter with the barbecue seasoning, coating both sides. Heat 2 tsp olive oil in the reserved pan over medium-high heat. Cook the chicken, turning regularly, for 4-8 mins until golden and cooked through. Remove from the pan and rest for 3 mins.
Step 6 — Get ready to serve
Halve the buns through the middle. Put on an oven tray, cut-side up, and bake for 5 mins or until lightly toasted. Drain the cucumber, discarding the liquid. Slice the chicken. Spread the buns with the burger sauce. Fill with the chicken, onion, tomato and cucumber. Serve the burgers with the potato wedges.