Fresh Tuna Niçoise Salad

Ingredients

• 2 tbsp (30 ml) olive oil
• 1 tsp capers, chopped
• 1 tsp (5 ml) apple cider vinegar
• 1 tsp (5 ml) whole-grain mustard
• 1 tsp tarragon, finely chopped, plus more for serving
• 1 lemon, zest finely grated
• 1 cup (120 g) green beans, trimmed and cut into 1-inch (2.5 cm) pieces
• 1 cup (140 g) cherry tomatoes, halved
• 6 kalamata olives, pitted and coarsely
• 1 piece fresh tuna, about 5 oz (140 g), 1 inch (2.5 cm) thick
• 1 tbsp (15 ml) olive oil
• 4 large Boston lettuce leaves, torn
• Fleur de sel (optional)