Tuna Everything Bagel

Name: Tuna Everything Bagel
Ingredients: 3 cups good quality canned tuna (packed in water), drained; 1/4 cup mayonnaise; 4 cornichons, chopped; 2 tablespoons chopped fresh dill; 1 tablespoon chopped fresh tarragon leaves; 2 tablespoons freshly chopped parsley leaves; 2 tablespoons capers, drained; 1 lemon, juiced; Kosher salt and freshly ground black pepper; 1/4 to 1/2 cup extra-virgin olive oil, or to taste; 2 everything bagels, sliced and toasted; 1/4 cup cream cheese; 1/2 red onion, thinly sliced crescents; 1 vine-ripened tomato, sliced; 1 seedless cucumber, sliced; 4 Bibb lettuce leaves