Find a good size banana leaf ( we have them all over in the yard) cut the middle of the leaf out, lay the leaf flat and put your fillet on it, then cover it with a layer of Mayo, salt and pepper to taste , add garlic powder and Greek seasoning, then cut the lemon in half , squeeze half of the lemons juice onto the fillet and slice the other half into 3 slices.
After slicing the onion into several pieces, layer on top the fish and then put the Lemon on top of that.
Now wrap the whole thing once with the leaf, and then another time the oposite direction with another piece of leaf.When it's sort of tight, tie it together with some bakers twine and put on the grill for about 20 minutes depending on how hot your grill is, I put mine just off direct heat to keep it from burning.Close lid on grill.
Open it up and enjoy.I imagine you could do this with any fish but we catch so many Blues , it's sad to see them all go into the crab traps.
If you like grits, we have ours with Guda cheese, a can of Rotel, Onions , peppers,and instead of water we make them with chicken broth.The best damn grits you will ever have.