Bluefish Grilled in Foil Packets

I've been cooking blue fish I had caught on
the grill in foil for over thirty years.
This is how I cook them with good results.

Ingredients:
3 medium red onions, peeled and sliced thick
6 plum tomatoes, ends trimmed, sliced in thirds
3 cloves garlic, peeled and sliced thin
1 tablespoon thyme leaves
Kosher salt and freshly ground white pepper
1/2 cup extra-virgin olive oil
1/3 cup chopped shallots
1/3 cup capers, strained
1/2 cup Dijon mustard
1 tablespoon green peppercorns
1/4 cup prepared horseradish, drained
1/3 cup chopped fresh dill
1/3 cup chopped fresh parsley
1/4 cup soy sauce
2 teaspoons lemon juice
6 6-ounce day-boat bluefish fillets, skinned and dark meat removed
Applewood or cherrywood chips, soaked in water

Directions:
Prepare a medium-hot grill (if cooking indoors, preheat a cast-iron sauté pan until it is very hot). Arrange the onion and tomato slices in one layer on a cookie sheet or in a roasting pan, and sprinkle with garlic
and thyme. Season with salt and pepper and drizzle with the olive oil. Allow to marinate for 30 minutes.

Remove tomato and onion from the marinade, allowing excess oil to drip off, reserving marinade. Place the slices over the hot coals and cook until charred (tomatoes and onions will char in the dry pan as well). Return the slices to the marinade, and set aside until ready to serve. (May be prepared in advance up to this point;
cover and refrigerate in the marinade overnight,
allowing them to return to room temperature before serving.)
Maintain the grill heat for the fish fillets.

Combine in a food processor the shallots, capers, mustard,
peppercorns, and horseradish, and process until puréed.
Add the dill and parsley, and pulse a few times to combine. Set aside.

Mix the soy sauce and lemon juice in a small bowl, and brush each fillet generously on both sides with the mixture. Cut 12 pieces of aluminum foil, approximately 15 inches square, to make six 2-layer packets. On the middle of each double-layered square, arrange equal amounts of tomato and onion, and drizzle with remaining marinade. Top with one seasoned bluefish fillet, and spread equal portions of the shallot-caper mixture over each fillet. Bringing two sides of the foil together above the fish, seal and roll down close to the food. Pinch the ends closed, and fold once or twice to seal tightly.

Move the coals to one side of the grill.
Transfer the foil packets to the grill away from hot coals,
cover the grill, and cook for 15 minutes.
Add some wet cherry or apple chips to the hot coals.
Open the packets, cover the grill,
and continue cooking for 3 to 5 minutes.