Pat the fish fillets dry with paper towels to ensure they crisp up nicely when fried.
Mix all-purpose flour, cornstarch, baking powder, and salt in a large bowl to create a dry batter mixture.
Pour sparkling water into the dry mixture gradually, stirring gently until a smooth, slightly thick batter forms.
Dip each fish fillet into the batter, making sure it's evenly coated on all sides.
Heat oil in a frying pan over medium-high heat until shimmering. Carefully lower the coated fillets into the hot oil.
Fry the fish for about 3-4 minutes per side, or until golden brown and crispy, then remove with tongs or a slotted spoon and drain on paper towels.
In a mixing bowl, combine shredded cabbage and grated carrot for the slaw.
Whisk together mayonnaise, lime juice, honey, and a pinch of salt to make the tangy dressing.
Toss the shredded vegetables with the dressing until everything is evenly coated and looks vibrant.
Warm the tortillas in a dry skillet or wrap in foil and briefly heat in the oven until they are soft and pliable.
Assemble the tacos by placing a crispy fish fillet inside each tortilla, then topping with a generous amount of slaw.
Serve the tacos immediately, allowing the crispy fish and cool slaw to create a delightful contrast in each bite.