Tuna Niçoise Salad

Dressing:
6 Tablespoons extra virgin olive oil
2 Tablespoons fresh lemon juice
2 Tablespoons freshly squeezed orange juice
2 to 3 teaspoons Dijon mustard
Coarse salt

Salad:
1 pound baby new potatoes, boiled and cooled
Coarse salt and freshly ground pepper
2 heads butter or other leafy lettuce
4 eggs, hard-boiled and cut in half lengthwise
½ pound haricot verts or thin green beans, blanched and chilled
1 red or yellow bell pepper, seeded and thinly sliced
1 pint cherry or grape tomatoes
½ English cucumber, thinly sliced
1 small fennel bulb, thinly sliced
13 ounces premium white meat tuna, drained
¾ cup Kalamata olives