First, make the dressing by mixing the lemon juice with ground cumin and stir in the red onion and season. Cover and leave to marinate for 1 hour.
To make the rice salad, pour the cooked brown rice into a large bowl and stir in the chickpeas, pistachio nuts, courgette and pomegranate seeds.
To finish the rice salad, stir in the marinated onion with its lemon and cumin dressing, taste and season with salt and pepper.
Blend the yoghurt and sumac ready to dress the cups.
Lay each cos lettuce leaf out on a platter and spoon the rice into each cup, now add the sliced beef, a dollop of the yoghurt dressing and a sprinkle of sesame seeds, season with pepper and serve.