How to Make It
Season the tuna generously with salt and transfer to a large resealable plastic bag. Add 1 cup of the olive oil, two-thirds of the garlic, the lemon zest, peppercorns, bay leaves and the canola oil. Seal the bag, pressing out the air. Refrigerate for 3 hours.
Pour the bag contents into a large saucepan and bring to a simmer. Cook over low heat for 7 minutes, turning the tuna if it's not completely submerged. Remove from the heat; let stand for 30 minutes. Using a slotted spoon, transfer the tuna to a plate. Pick off the peppercorns and flake the fish. Discard the bay leaves and oil.
Meanwhile, in a small saucepan of boiling salted water, cook the green beans until crisp-tender, about 2 minutes. Drain and cool under cold running water. Pat the beans dry and transfer them to a small bowl; add the lemon juice and 1 tablespoon of the olive oil. Season the beans with salt.
In a mini food processor, combine the remaining garlic with the olives, anchovies and basil and process until finely chopped. Add the remaining 1/4 cup of olive oil and process to a chunky paste. Add the mayonnaise and pulse to blend.
Spread the olive aioli on the focaccia rolls and fill the sandwiches with the roasted peppers, green beans and tuna. Close the sandwiches and serve.