Preheat a fryer or a deep pot halfway filled with oil to 375 degrees F.
Mix 1 of the packages of batter, but only use 1/2 the required amount of water and use beer for the remaining amount instead. Add the beer until the batter becomes almost like a heavy cream consistency.
Using the other package of batter add salt and garlic powder, coat cod pieces with the dry mix, then dip into prepared batter. Deep-fry for about 3 minutes, or until golden brown and cooked through.
Place fried cod pieces on warmed corn tortillas, add white sauce to fish, a little shredded cabbage and a squeeze of lime, to taste.