Tunisian Tuna Salad Sandwiches

Name: Tunisian Tuna Salad Sandwiches
Ingredients: 2 7-oz. cans of water-packed tuna; 1 large Yukon Gold potato, peeled, cubed (½-inch pieces); 1/4 cup extra virgin olive oil, plus more for drizzling; 1/4 cup lemon juice; 4-5 tablespoons fresh parsley, chopped; 1/4 cup capers, drained and rinsed; 1 tablespoon green olives, sliced (optional); 2 large hard-boiled eggs, sliced; 2 tablespoons Harissa (Tunisian hot chili sauce); 2 crusty hoagie rolls; kosher salt to taste; freshly ground black pepper