If you cannot do without a steak -but do not eat meat-, tuna is what you need. I don't know any other kind of fish that comes closer to a piece of "moo'!
Grilled in a iron skillet pan is definitely the best way to go. Make sure to first heat it up to piping hot temperature. Then add a few drops of (coconut) oil and give it a 'vuelta y vuelta' (Argentine's use this term for 'searing' meat a few seconds on one side and then a few more on the other).
You like your tuna to be 'more than just pink', even a bit raw in the inside, otherwise it will dry out and taste like...cardboard :-D
Depending on the thickness of your steak, it will take a few seconds more or less (keep an eye on the side of the piece and watch the heat penetrate the fish).
Some (preferably Himalayan) salt and pepper from the mill will do. But if you are looking for something to kick your taste buds, here is an amazing relish for you to try out:
Ingredients (for 2 tuna steaks)
•4 sundried tomatoes in oil -cut in strips
•1 medium shallot - finely chopped
•1 anchovies in oil -minced
•1 tsp of agave syrup
•2 tbs virgin olive oil
•1 1/2 tbs of red wine vinegar
•2 tbs of dry sherry (if you use medium dry sherry instead, you can omit agave syrup)
•5 basil leaves
Putting it together
•put all ingredients in a bowl and let all the ingredients soak up flavors for at least 1 hour
•just before serving, take some scissors and cup up the basil leaves in the mixture and stir
There are different ways to serve this:
a) You can either make individual steaks and top it with the relish or
b) You can slice the tuna steaks, arrange them carefully in a flat dish and then pour the relish on top. This way the tuna will get cold quickly, but that's fine. It will taste awesome as a 'cold' tapa dish as well!