1. Start by preparing the mango salsa. In a medium bowl, combine the diced mango, red onion, jalapeño, cilantro, and lime juice. Season with salt to taste, and set aside to let the flavors meld.
2. For the fish, pat the fillets dry with paper towels and cut them into taco-sized pieces.
3. In a large bowl, whisk together the flour, baking powder, salt, and black pepper. Gradually add the cold sparkling water, whisking until you have a smooth batter.
4. Heat about 1 inch of vegetable oil in a deep skillet over medium-high heat. The oil is ready when a drop of batter sizzles upon contact.
5. Dip each piece of fish into the batter, allowing the excess to drip off, and carefully place it into the hot oil. Fry in batches, about 3-4 minutes per side, until golden and crispy. Transfer to a paper towel-lined plate to drain.
6. Warm the corn tortillas in a dry skillet over medium heat, about 30 seconds per side, until pliable.
7. To assemble, place a handful of shredded cabbage on each tortilla, top with a piece of crispy fish, and finish with a generous spoonful of mango salsa.

One tip I picked up from my mom: always taste the salsa before serving. Sometimes, a little extra lime juice or a pinch of salt can take it from good to great.