Go to Walmart and get some "Cachetes de Mero" (Mero cheeks, really!) they look like nuggets and are wonderful. When you clean them make sure to remove the little bone on the side and you will have boneless fish nuggets. Otherwise, Cod is great or any good fish fllet you like and could be Snapper, etc.
Make the beer batter: Any beer will do. Put flour in a bowl with a teaspoon of red chile powder and pour some beer in while mixing. Batter should be thick so take care when you add the beer so it doesn't get too runny, so it will stick to whatever, ok? About 1.5 cups of flour per beer I guess but go easy.
Get some oil in a pan ready to fry and put the cheeks (or fish cut in nugget sizes)into the batter and then in the oil and watch until they get golden. This batter covers really well and gets really crispy, great for all kinds of fish and veggies (like tempura)
When you've fried the fish it's time to build the tacos. Get good tortillas (best ones come from Mega Comercial), lay 3-4 pieces of fish, some lemon and you can try some sauce (green salsa is good or habanero is better), lettuce and pico de gallo (tomato, onion, cilantro) on top and you're good to go....
If you use the batter for fillets, here's a trick: Put the fish in the hot oil and it will sink and stick to the bottom of the pan. RESIST THE URGE TO UNSTICK THE FISH or it will rip the batter off, instead wait a little while and it will unstick itself when it is ready and you will have a whole fillet with complete coverage.... take it easy, it's worth it.