Stuff the fish with everything apart from the salt and lemon
Place between two layers of tin foil on a foldable grill
Grill over medium-hot coals 8 minutes each side or until cooked un the centre.
When done sprinkle with salt and a squeeze of fresh lemon juice
As cooking over coals is an ancient way and you really need the feel for it by practicing. If you don't cook over coals a lot or have little experience just check the fish for doneness every now and then by inserting the tip of a knife into the thickest part of the flesh and very carefully and quickly testing the temperature on your bottom lip) It should be the temperature of a lukewarm cup of tea at least. If you have a temperature probe then 55C is what you looking for. Careful not to overcook the fish as it will become dry. Undercooking is easily fixed while overcooking not so much.