In a small bowl mix together the oil, lemon juice, fresh chopped dill, sumac and salt and pepper.
Place the salmon skin side down on a plate or shallow dish and cover with the oil mixture, rubbing it well into the flesh of the salmon.
Leave in the fridge for up to 24hrs or cook straight away.
Place the fish, skin side down on the barbecue grid, over coals which are beginning to lose their heat. (Gentle heat is best)
If the barbecue is a dome Weber type then place the lid on and leave to cook for 10/15 minutes. If there is no lid on the barbecue then make a little dome with a piece of foil, enough to cover the fish and help keep the steam in.
The skin will get very crispy and brown when cooked but the flesh will remain succulent and flake easily.