Heat the vegetable oil in a heavy-bottomed saucepan until a breadcrumb sizzles gently.
Dredge chicken strips in flour, dip in egg, and coat thoroughly with couscous.
Deep fry the chicken for 5 minutes until golden and cooked through.
Drain the fried chicken on kitchen towels.
Heat olive oil in a pan and fry leeks and chilli for 1 minute.
Add tomato, purée, ketchup, vinegar, sugar, and half the coriander, then cook for 2 minutes.
Stir the cooked couscous into the tomato sauce and season with salt and pepper.
Serve the chicken over the spicy couscous and garnish with remaining coriander.