Rub tuna with olive oil and season with salt and pepper.
Heat a griddle pan or a heavy based frying pan tull smoking hot.
Sear tuna for about 3 to 4 minutes on each side depending on the thickness of the fish - the centre should remain pink.
Meanwhile pour the oil that's on the surface of the pesto into a small pot, heat and add the tomatoes. Cook for about a minute and add remaining pesto. Cook to heat through.
Toss in olives, water and parsley and cook for about 3 minutes or till thoroughly heated through.
Season to taste, spoon over tuna and serve with a side dish of mixed beans.
Tip: How to de-pip an olive: Make a shallow slit in each olive and, using the broad flat side of a kitchen knife, press down firmly on each olive. The pip will be loosened and can simply be popped out.