This is a great appetizer or lunch. Nicoise denotes dishes prepared in the cooking style found in and around Nice. Ingredients frequently used in this cuisine include tomatoes, olives, garlic and anchovies.
Whisk together the tarragon, cider vinegar, Dijon mustard, olive oil, salt, pepper, garlic, parsley and lemon juice in a bowl. Use half of the dressing to marinate the tuna and reserve the other half to pour over finished dish.
Marinate the tuna with half of the dressing in a covered, shallow non-reactive dish. Cover and refrigerate and let tuna marinate for 20 minutes. Thread each of the marinated tuna on a skewer. If using wooden skewers, soak in water first.
Preheat grill on high.
Remove tuna from marinade and pat dry. Grill the tuna skewers about 1 minute per side, grill should be hot so tuna form grill marks readily – it looks nice for presentation. Tuna will be cooked to rare. Remove from grill.
Combine the potatoes, green beans, radishes, olives, anchovies, eggs and tomatoes on a serving bowl or platter. Pour over the dressing. Add tuna skewers and serve.