Brush the tuna steak with an even coating of oil and season with plenty of black pepper to taste. Heat a frying pan until hot and press the tuna steak onto the pan to sear. Cook on each side for 1 minute and then continue to cook until the tuna is at the preferred doneness – arguably it is at its best when still pink in the middle. Remove from the pan, allow to stand for a couple of minutes and then slice into long strips.
Lay a tortilla wrap on a bread board. Mix the red onion, chilli dipping sauce and yoghurt together. Divide this mixture between the two wraps and spread across the diameter of the wrap. Sprinkle with coriander leaves and season with salt. Arrange the tuna slices on top and finish with a handful of rocket leaves. Season to taste.
Wrap the tortilla by rolling tightly from one side to the other and folding in the edges to make a complete wrap. Cut in half across the diagonal and stand upright to serve. Hand a lime wedge on the side.