The fish is cooked in a foil packet on the grill. The rice side dish, also grilled in a foil pack, is a mixture of tomato, onion, and fresh basil.
Thaw fish, if frozen. Rinse fish; pat dry. If you like, remove head and tail. Lightly grease a 24x18-inch piece of heavy-duty foil. Place fish on foil. Lay open fish and season cavity lightly with salt and black pepper. Arrange half of the sliced lemon and a thyme sprig in cavity.
Close fish. Top with remaining lemon slices and thyme sprig. Bring up 2 opposite edges of foil and seal with a double fold. Fold remaining edges together to completely enclose fish, leaving space for steam to build.
In a medium bowl combine rice, onion, tomato, basil, 1/4 teaspoon salt and 1/4 teaspoon pepper. Tear off a 36x18-inch piece of heavy-duty foil; fold in half to make an 18-inch square. Place rice mixture in center of square. Bring up 2 opposite edges of foil and seal with a double fold. Fold remaining edges together to completely enclose rice, leaving space for steam to build.
For a charcoal grill, arrange medium-hot coals around edges of grill. Test for medium heat in center of grill. Place fish in center of grill rack. Cover and grill for 10 minutes. Add rice packet next to fish but not over coals. Grill 25 to 35 minutes more or until fish flakes easily when tested with a fork and rice is heated through. (For a gas grill, preheat grill. Reduce heat to medium. Adjust for indirect cooking. Grill as above.)
To serve, use 2 large spatulas to transfer foil packet from grill to a large serving platter. Serve fish with rice mixture. Garnish with lemon wedges and additional fresh thyme sprigs, if you like. Makes 6 servings.