Tips for cooking seared tuna just right?
With seared Tuna the point is to create a charred crust while leaving the inside mostly raw. It's very similar to cooking a steak rare in that the secret is a very hot pan and a short amount of time. So get your pan as hot as you can, coat the cooking surfaces of the tuna steaks with a bit of oil with a high smoke point (corn, canola, peanut - not olive oil or walnut oil), then fry the tuna for as little time as you can get away with. I'd think 45-60 seconds per side. In case you are wondering the oil forms a good heat contact with the tuna, improving conductivity, it's not for any flavor effect. 

Now you may have a stove that doesn't get the pan hot enough in which case it takes too long to form a crust and the inside cooks more than you like, in which case you can try:


Not letting the tuna thaw completely. If it's still a teensy bit frozen in the middle the heat from the cooking will thaw it, not cook it. You could also try it straight out of the fridge
Use a cooking torch. You can also use a plumbing torch, it's the same thing except much cheaper