Prepare the tuna confit. Combine the tuna steaks with 2 sprigs oregano, 1 sprig rosemary, 3 garlic cloves, 10 black peppercorns, and 2 chili de arbol in a small pot. Add enough olive oil to generously cover the tuna. Bring to a simmer over low heat and cook until the tuna starts to turn grey. Simmer for another 5 minutes then turn off the heat and let the tuna cool in the oil.
Meanwhile, make the olive tapenade. Use a food processor to pulse 1 cup olives, 3 anchovy filets, zest and juice of 1 lemon, 2 garlic cloves, ½ teaspoon red pepper flakes, and 1 teaspoon red wine vinegar until it forms a paste. Stir in 2 tablespoon olive oil and season with salt and pepper.
Make the lemon aioli. Whisk together ¼ cup mayonnaise with 1 teaspoon lemon juice, ½ teaspoon lemon zest, salt, and pepper.
Assemble the sandwiches. Lightly toast the bread and spread the olive tapenade on one slice and the lemon aioli on another. Top the bottom slice with piquillo peppers followed by the tuna. Season the tuna with salt, pepper, and a squeeze of fresh lemon juice. Top with capers, thinly sliced shallots, and arugula. Top with the remaining bread and serve.