Mediterranean Tuna Salad

Name: Mediterranean Tuna Salad
Ingredients: 2 teaspoons dijon mustard; Grated zest and juice of 1 lemon; 1/3 cup extra-virgin olive oil, plus more for brushing; 1/4 cup chopped fresh dill; Kosher salt and freshly ground pepper; 1 12-ounce can solid white tuna in water, drained and flaked; 1 14-ounce can chickpeas, drained and rinsed; 1 Kirby cucumber, seeded and chopped; 1 bunch scallions, sliced; 1 pint cherry or grape tomatoes, halved; 2 pieces pita or naan bread; 1 head romaine lettuce, shredded