Wash and slice the pepper. Place it in a bowl and add olive oil, salt and lemon.
Add the tuna steaks to a pre-heated pan. Sear the tuna steaks for about 3-4 minutes, then repeat on the other side. Add a pinch of salt. You can lengthen the cooking time if you want to make sure that the tuna is fully cooked through.
Add the seasoned pepper into a flat serving dish, then add the cooked tuna steaks.
Season with more olive oil, white wine vinegar, sliced spring onion, black olives, lemon zest and parsley.
Let the dish rest to marinate for at least 30 minutes before serving.