I made this for dinner last night and it was really yummy! I had mine very rare but my mom isn't a fan of raw fish so hers was well done - it worked both ways.
The proportions are for 3 medium sized tuna steaks, but there was plenty of fish for 4 people!
For the marinade, mix together:
3 tbsp soy sauce (I use low sodium but you don't have to)
1 tbsp balsamic vinegar
1 tbsp sesame oil (you could use olive or canola if you want)
1 tbsp lemon juice
1 tbsp crushed garlic
1/2 tbsp crushed ginger
Coat the tuna steaks in the marinade and let them marinate in a covered container for as long as you can - I did it the night before and just put them in the fridge, but you don't need to wait that long. 20 mins should be good.
To cook, heat a grill or frying pan until it's really hot, almost smoking, and sear the steaks on both sides - 1-2 mins per side for rare (or less, I love rare tuna!) or 2-4 mins per side if you like it more well done. Let the steaks rest for a few mins before eating, then serve.
I had mine with asian coleslaw (no mayo, just a vinegarette dressing) and the green beans I posted last week. Delicious!