FlyFishinOK, this is known as "Redfish on the Half-Shell". I haven't tried it, and would have to research it a bit to give you the full run-down. However, if you close the lid on your grill, you create an "oven" effect and trap hot air inside. This would help to cook the cut side. On the flip side, you can start the fillet on the cut side, just enough to "mark" the flesh with grill marks, then flip it so the skin-side is down and finish the cooking that way.
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