IMHO, you need to keep carbs away from tuna otherwise the fairly delicate flavour can get ruined.
This is a Rick Stein recipe which is fantastic - it really enhances the flavour of the tuna. We've been making it for several years - it's still my favourite meal:
Seared Tuna, Rice Noodle & Coriander Salad
2 tuna steaks
6 tbsps dark soy sauce
4 tbsps balsamic vinegar
1 tbsp sesame seeds
bunch coriander
6 spring onions trimmed
coarsely grated juice & zest of 1 lime
2 tsps thai fish sauce
3 fl oz water
2 tsps roasted sesame oil
2 tbsps sunflower oil
3 oz rice vermicelli noodles
3 green chillis, seeded & finely chopped
2 tbsps japanese pickled ginger shredded (don't worry if you don't have)
small bunch garlic chives, chopped (can be difficult to get hold of, don't worry if you don't have)
1 bunch watercress broken into sprigs
Instructions
Preheat the grill to high. Spread the sesame seeds on a baking tray and toast, shaking occasionally, until golden.
Pick the leaves off the coriander and discard the stalks, (you need about 6 tbsps in all).
Thinly slice the spring onions on the diagonal. Mix together the lime juice, fish sauce, water, sesame oil and sunflower oil with the sesame seeds, coriander, spring onions, lime zest, chilli, ginger, chives and watercress.
Bring a pan of water to the boil, drop in the noodles and take off the heat. Leave for 3 mins (whilst that's cooking, start the tuna) drain well and tip back into the pan. Cover and keep warm.
Heat a heavy based frying pan until very hot. Brush with a little oil. Add the tuna steaks and cook for 2 mins on each side. Add the soy sauce and balsamic vinegar to the pan and boil vigerously, turning the steaks once, until they become covered in a rich brown glaze. Remove from the heat and keep warm.
Pile some of the salad into the centre of 4 warmed plates. Slice each tuna steak into 3 on the angle and put on top of the salad. Serve remaining salad seperately.