2) Bring the stock, carrots, onions and tomatoes to the boil and simmer for an hour.
3) Melt butter add garlic, onion and crushed lemongrass and sweat, do not colour. Add the barley and then the stock, a ladleful at a time, until barley is almost cooked, approx 40 minutes.
4) Add the remaining stock, take out the lemongrass, add the tomatoes, parsley and chopped lobster and season. Leave to one side.
5) Cook the tuna steaks with olive oil and season. Put the risotto in a bowl with the tuna on top, squeeze lemon juice over and serve.