Foryoueats: Mayo-Free Mediterranean Tuna Salad Sandwiches Recipe

Ingredients

• 1/2 medium red onion (about 4 ounces; 110g), thinly sliced
• 1/4 cup (60ml) red wine vinegar
• 20 ounces (560g) oil-packed tuna, preferably ventresca (see note), drained and flaked by hand into roughly 1/2-inch pieces
• 1 stalk celery (about 3 ounces; 85g), sliced thinly on the bias
• 1/4 medium bulb fennel (about 1 ounce), cored and thinly sliced
• Handful flat-leaf parsley leaves, roughly chopped
• 2 tablespoons (30ml) drained brined capers
• 1/4 cup (60ml) drained pitted briny black or green olives, quartered lengthwise
• 1/4 cup plus 2 tablespoons (90ml) extra-virgin olive oil, plus more as needed
• 2 tablespoons (30ml) fresh juice from 1 lemon
• 1/2 teaspoon (3ml) Asian fish sauce or very finely minced oil-packed anchovy fillets (about 2 small fillets)
• Kosher salt and freshly ground black pepper
• 8 slices rustic sandwich bread, such as a Pullman loaf, brushed with olive oil and toasted
• Arugula, for garnish