1.Combine herbs, garlic, chilli, rind, spices and oil in a large bowl. Place half the herb mixture into a medium jug; cover, refrigerate. Combine lamb with herb mixture in bowl. Cover; refrigerate 3 hours or overnight.
2.Cook lamb on a heated oiled barbecue (or grill or grill pan), brushing with herb mixture, about 25 minutes.
3.Meanwhile, to make warm couscous salad, combine couscous and the boiling water in a medium heatproof bowl; cover, stand 5 minutes or until water is absorbed, fluffing with a fork occasionally. Stir in remaining ingredients; season to taste.
4.Stir juice into reserved herb mixture; season. Cut lamb into pieces; serve with couscous and reserved herb mixture.
Lamb riblets are just small cuts from the rib area.