Preheat the oven to 200°C.
Finely mince the dill, finely grate the garlic, add the garlic and half the dill into a bowl with the mustard and a generous drizzle of olive oil. Season generously with salt and plenty of freshly cracked black pepper.
Using scissors, snip the chicken into 3cm chunks, toss into the marinade. Thread the chicken onto some metal skewers. Place the skewers onto a baking tray and roast until cooked through,15-20 mins. Switch the grill onto high and grill until starting to char, flip and continue cooking until charred in places on both sides of the skewers.
Meanwhile, quarter the radishes and chop the cucumber into 1cm chunks. Add to a bowl, with the juice of the lemon and olive oil. Season with salt and pepper. Crumble the feta and toss through the salad.
Reheat the flatbreads, top with the skewers, salad, the rest of the dill, and a dollop of Greek yoghurt.
