In a large bowl, toss the chicken thighs with salt, pepper, shawarma seasoning, and the juice of two lemons. Add garlic, potatoes, red onion, olive oil, capers, oregano, and lemon wedges. Mix thoroughly and let rest for 30 minutes to one hour.
Preheat your oven to 210°C/190°C fan or gas mark 7. Spread the marinated mix onto a large sheet pan. Ensure it’s evenly spaced to avoid overcrowding. Roast for 30 minutes until the chicken is golden brown and the potatoes are soft.
While the chicken bakes, dice the cucumber and combine it with Greek yogurt, chopped dill, mint, spring onion, and lemon juice. For added depth, mash two roasted garlic cloves into the mix. Season with salt and pepper.
Once the chicken and potatoes are ready, arrange the tzatziki sauce on a serving plate, layer the chicken and potatoes on top, and sprinkle crumbled feta and extra dill. Serve immediately.