Well, you mentioned "blackening" and someone else mentioned Tuna steaks. Blackened Tuna is truly a gift from the gods, if you ask me.
Blackened Seasoning Mix
2 T paprika
5 t salt
2 t onion powder
2 t garlic powder
2 t cayenne
1 ½ t white pepper
½ t black pepper
1 t thyme
1 t oregano
Mix all ingredients well, and place in a shaker (I use a Parmesan cheese dispenser like the pizzerias use.). DO NOT breathe in the “dust cloud” while mixing the spices together!
To properly blacken (cook) the tuna steak, please remember that this is best down outside, using a Coleman Camp stove and a cast iron skillet. I will do this inside, but I don't really get the heat up to high, and don't create a lot of smoke. The smoke has been referred to a "Cajun Bomb" by some of my co-workers.
You'll need some clarified butter. If you know how to make it, great. You can get by with using vegetable oil, but the flavor will not be quite the same.
Heat the pan until it's hot on the camp stove. Make sure to get your mise en place ready, and have the fat handy, seasoning mix nearby, and the tuna steak on a plate, platter, or something else similar. While the pan is heating, season the tuna steak with the seasoning mix. How much you use will determine how hot and spicy it is. How hot you can tolerate it will be trail and error.
Once the pan is hot, add some of the clarified butter or veggie oil. Lay the seasoned tuna steak on the pan, seasoned side down. While this cooks, season the other side of the tuna, which is now facing up. Cook for a few minutes. Flip once, adding a little more fat to the pan right before you flip it. Cook to desired doneness. I prefer a medium tuna steak.
It's been awhile since I last cooked tuna steak like this, so I can't really give you temperatures and times. I always cook by feel, anyway. I poke the tuna steak with my finger to feel if it's still slightly "soft" inside. Again, this is a trail-and-error process that I've learned working in restaurants.
Paul Prudhomme's first cookbook, "Louisiana Kitchen" describes the process, although I always thought his heat was up to high. He wanted the pan so hot you were developing ash IN the pan, from the season on the pan burning. I prefer a lower heat, as it doesn't flare up and burn as much, it's a slower process (doesn't burn into inedibility as fast), etc.
I recently reheated some ultra-rare blackened tuna (so that it was blackened medium) and ate it. Well, my DW wanted some, then my oldest step-son wanted some! He's the pickiest eater here.