3 cups olive oil
4 or 5 sprigs fresh thyme
1 lemon, juiced and zest peeled off in strips
2 large bay leaves
2 large cloves garlic, smashed
1 1/2 pounds tuna steaks (such as ahi or yellowtail), 1 inch thick
2 ribs celery with leafy tops, finely chopped, or 1/2 small bulb fennel, finely chopped
1/2 red onion, finely chopped
1 small fresh red chile, seeded and finely chopped
1/2 small red bell pepper, finely chopped
1/4 cup fresh flat-leaf parsley leaves, chopped
Leaves from 2 or 3 sprigs fresh tarragon, finely chopped
2 to 3 tablespoons capers, drained and rinsed
1/4 cup niçoise or other brine-cured black olives, pitted
Rachael Ray Seafood Seasoning or Old Bay seasoning
6 ounces very sharp white cheddar cheese or Gruyère cheese, shredded on the large holes of a box grater
4 brioche rolls or lobster rolls, split
In a deep skillet, combine the oil, thyme, lemon zest strips, bay leaves, and garlic. Bring to a gentle boil over medium-high heat. Remove the pan from the heat and add the fish. Let stand 20 minutes. Transfer the fish to a plate to cool. Reserve the poaching oil and let cool. Strain into a clean jar.
Whisk together the lemon juice and 1?3 cup of the reserved poaching oil; season with salt and pepper. Add the celery, onion, chile, bell pepper, parsley, tarragon, capers, and olives. Flake the fish with 2 forks. Season with a little seafood seasoning, add to the dressing, and toss to combine.
Make-ahead: Cover and refrigerate.
Night of: Remove the salad from the refrigerator.
Preheat the broiler with a rack in the center of the oven.
Place the split rolls on a baking sheet. Pile the tuna salad on the roll bottoms and top with the cheese. Broil to toast the roll tops and melt the cheese, about 2 minutes. Serve hot.