1.To make chermoulla sauce: Blend or process herbs, garlic, chilli and ground spices until combined. Add juice and oil; process until smooth. Transfer to a medium bowl; stir in yoghurt. Season to taste.
2.Cut each onion into 8 wedges, keeping root ends intact. Combine onion, zucchini and asparagus with half the oil in a medium bowl.
3.Cook vegetables on a heated barbecue grill plate until charred and tender. Transfer to a large plate; cover to keep warm.
4.Rub salmon with remaining oil; season. Cook salmon, skin-side down, on heated barbecue flat plate until skin crisps; turn, cook until just cooked through.
5.Serve salmon with sauce and vegetables.
You can prepare the vegetables and sauce up to a day ahead; keep the sauce, covered, in the refrigerator.Note