In a bowl, mix yoghurt, lemon juice, garlic, cumin, coriander, salt, and pepper. Coat chicken tenderloins and marinate for at least 20 minutes (or overnight).
Place couscous in a bowl. Pour over 1¼ cups of boiling water, cover, and let stand for 5 minutes. Fluff with a fork and season lightly. Then stir through the chickpeas.
In a medium bowl, combine cucumber, onion, tomatoes, radish, parsley, dill, lemon juice, olive oil, and sumac. Toss to combine.
Heat a large non-stick pan or grill pan over medium heat. Cook marinated chicken for 4–5 minutes per side or until golden and cooked through. Rest before slicing.
Mix yoghurt, mayonnaise, lemon juice, and chopped dill until smooth.
Spoon chickpea couscous into each bowl. Add chicken slices and salad. Drizzle with the dill yoghurt sauce.