Preheat the oven to 180°C. Heat a griddle pan over a medium high heat with a little olive oil. Throw your chopped cauliflower and leeks onto a baking tray with the smoked paprika and a drizzle of olive oil and place into the oven for 20-30 minutes.
While the vegetables are cooking mix the chicken with the sumac, aleppo pepper, salt and pepper in a bowl. When the griddle pan is hot add the chicken and spread into a single layer. After a few minutes add the red onion. Allow the chicken and onion to cook for about 10-15 minutes, turning occasionally, until the chicken is cooked through and the onion is softened.
While everything is cooking add the cous cous to a bowl and cover it with double its volume of boiling water. Cover the bowl with a clean tea towel and allow to sit for 10 minutes until all the water is absorbed and the cous cous can be fluffed with a fork. To finish, mix in all the remaining tabbouleh ingredients.
Serve the chicken, tabbouleh, leeks and cauliflower with pitta bread, greek yoghurt and salad leaves.