Cut the fish into 1 1/2-inch chunks. (Reserve 1 fillet and refrigerate for the online Round 2 Recipe, Ceviche.)
To make the batter, whisk together the flour, baking powder, and salt in a medium bowl. Whisk in enough water, about 1 to 1 1/2 cups, until the mixture is the consistency of pancake batter.
Heat the oil in a deep skillet over medium heat to 360 degrees F.
When the oil is hot, working in batches, dip the fish pieces into the batter and carefully add them to the hot oil. Cook the fish until golden brown on both sides and the fish is cooked through, about 4 to 6 minutes total. Remove from the pan and drain on to a sheet tray lined with a paper bag or paper towels.
To make the sauce, whisk together the mayonnaise, sour cream, hot sauce, lime juice, garlic, and 2 tablespoons cilantro in a small bowl. Taste and adjust seasoning with salt and pepper.
Wrap the tortillas in a damp towel and microwave on medium for 1 minute to warm. Put about 1/4 cup of the shredded cabbage on each tortilla. Put 3 pieces of the fried fish on top of the cabbage, then top with some sauce. Arrange the tacos on a serving platter and garnish with a sprinkle of cilantro. Serve immediately.