Fresh tuna has a meaty texture and a taste that's completely different from the canned variety (although tuna canned in olive oil is a delicacy in its own right). It is delicious served raw (in sushi or sashimi) or lightly seared, so it's still pink and moist inside. Don't waste an expensive piece of tuna by overcooking it.
Tuna tataki (pictured)
This dish couldn't be easier. Choose one or two long slabs of tuna that are 5-6cm wide and 2-3cm thick (triangular pieces are fine too). A shop specialising in Japanese ingredients, such as Uny, City'super or the basement grocery store in Sogo, should be able to supply you with what you need. If cooked correctly, the fish will be seared on the outside and cool and raw inside. For a light meal, serve the fish with steamed Japanese rice or cold noodles with dipping sauce and some Japanese pickles, such as seaweed or cucumber. It can also be served as an appetiser.
250 grams tuna fillet, in one or two pieces
About 15ml cooking oil
2 tsp sesame seeds (preferably a mixture of black and white)
1 spring onion, white and pale green parts only, cut into thin rounds