To make the dressing, mix the red wine vinegar, olive oil, parsley, chives, garlic, salt and pepper together.
Place the tuna in a shallow dish and pour over half of the dressing, and leave to marinate for approx. 90 minutes, tossing the marinade from time to time.
Cook the tuna steaks on a griddle pan for approx. 2 - 3 minutes on each side, and once removed cut into slices.
Lay the lettuce leaves onto a large plate and add the onion, tomatoes, potatoes and beans, along with the tuna slices.
Add the eggs, olives and basil leaves, and drizzle over the remaining dressing.