Normally one would use larger pieces of fish, and more extreme heat, but if you're doing this indoors in the winter you don't really want to do this the "right way" as you'll smoke up the house. Blackened seasoning + rocket-hot cast iron pan = fire alarms
You can have all the flavor though, as the seasoning is the same either way. Turned out really well, I must admit. I think I paid about $16 for this at Lone Star, maybe $4 at home. Had all the strong, hot flavor I was after.
1 Tbsp thyme
1 Tbsp oregano
1 Tbsp black pepper
1 Tbsp paprika
1 tsp cayenne pepper
1 tsp garlic powder
1 tsp salt
1 tsp onion powder
Melt some butter, brush onto the fish pieces (I used bluefish, aka Pollock). Dust with seasoning, and drop into medium-hot cast iron fan (make sure the range hood fan is on). Turn when black and a little crispy, simple.
Normally, you'd have your gas grill outside nice and hot, preheat your cast iron inside, carefully transfer outside to the grill with double-layer oven pads, and do the cooking part out there using crazy-high heat.
Served with a pilaf and some boiled carrots. Garnished with a pinch of pine nuts.