2.Meanwhile, blend or process avocado, juice, half the oil, garlic, tahini, cumin and half the sumac until smooth. Transfer to a medium bowl; season to taste. Cover tightly.
3.Season fish; drizzle with remaining oil and sprinkle with remaining sumac. Cook fish, skin-side down first, on a heated oiled barbecue (or flat plate or grill) over medium heat for 3 minutes each side or until just cooked through. Transfer to a plate; cover to keep warm.
4.Serve fish with salad, topped with avocado cream and lemon wedges on the side.
5.Place the water and barley in a medium saucepan; bring to the boil. Reduce heat; simmer, covered, for 35 minutes or until tender. Drain; cool. Combine vinegar and oil in a large bowl. Just before serving, add barley to bowl along with the remaining ingredients; toss gently to combine. Season to taste.
We used barramundi in this recipe but any thick or firm white fish fillet will be fine. You can use pearl barley for this recipe, if you like. Barley can be cooked several hours ahead. The avocado cream can also be made several hours in advance. Store separately in the fridge.