I used (and generally, unless I've really got myself together, I use whatever I've got around the house):
Cajun Seasoning (Joe's stuff)
Hot Sauce (Cholula Chili garlic, in this case)
Chipotle Chili Powder
Also, I made tomato/onion based salsa, and some brown rice, which were fine, but nothing special, and probably easily replaced with your favorite fish taco toppings.
I cut the mahi into 7 strips - about 1/2" - 3/4" thick, and 3" long or so.
For a fast marinade, I mixed about 1/3 of a cup of olive oil, with a couple tbsp lemon juice, and a tsp of hot sauce, then spiced with some liberally with chipotle chili powder, black pepper, pinch of kosher salt and just a bit of cajun seasoning.
You may have figured out by now that I'm not real big on precise measurements.
After blending thoroughly with a fork, I tossed the mahi strips in the marinade (just enough to cover the mahi strips with a nice layer), and let sit at room temperature for about 25 min.
Then, I made a light dusting for the fish - 2 parts flour to 1 part cornmeal (just under a cup, total), with a couple tsps each cayenne, garlic powder, onion powder, black pepper, paprika and a pinch of salt. Each fish strip was taken from the marinade and rolled them through once to coat lightly.
Lastly, I sauteed on both sides for about 3 minutes total (golden brown all around).
The results were surprisingly tasty - nice textured crust which complemented the spicy, slightly tart flavors underneath, and the firm, mild mahi that held up nicely. I got just a little hint of a saucy layer between the fish and crust, which was a nice surprise. Next time I try this, I might think about using a little lighter fish like cod, and probably smaller pieces - to be a little more taco friendly.