Cook the fish. Place your grill over the fire. Let it get extremely hot so the fish does not stick. Season the fish, inside and out, with salt. Stuff the fish with garlic, lemon, and tarragon. Once the grill is hot allow for the fire to calm down and maintain the heat without the flames. Lightly rub the outside of the fish with olive oil. Place the fish on the grill and cook until barely cooked through, about 4 minutes per side. Allow the fish to rest, and finish cooking for 5 minutes. Serve with corn and scallions on the side, and spoon the sauce over the fish.