Place 4 cups shredded cabbage in a colander or strainer and sprinkle with ½ teaspoon kosher salt. Massage and squeeze the cabbage to help release its liquid and begin wilting. Set aside to drain for about 15 minutes.

Squeeze the cabbage of its excess liquid one handful at a time, and transfer to a large bowl. Add 1 grated carrot, 2 to 3 thinly sliced scallions, and ½ to 1 seeded and minced jalapeño (if using). Toss to combine.

Add 2 tablespoons mayonnaise, 1 tablespoon freshly squeezed lime juice, and 1 minced garlic clove. Toss to combine. Taste and season with sugar, honey, or agave nectar (if using), kosher salt, and black pepper as needed.

Combine ⅓ cup all-purpose flour, 1 teaspoon kosher salt, ¼ teaspoon freshly ground pepper, and ⅛ to ¼ teaspoon smoked paprika or chipotle powder in a shallow container. Pat 1 to 1 ½ pounds of fish dry with paper towels, then dredge it in the flour mixture until evenly coated.

Heat 2 tablespoons vegetable oil in a heavy pan over medium-high heat until shimmering. Add the fish in a single layer, cooking undisturbed until golden-brown on the bottom, about 2 to 3 minutes. Carefully flip the fish and continue cooking until the second side is golden brown and the fish flakes apart easily, 2 to 3 minutes more. Transfer to a plate and flake into large chunks.

Heat the corn tortillas in a heavy, dry pan until soft and warm. Wrap them in a clean kitchen towel as you go. Serve the fish with the tortillas, slaw, cilantro, sliced avocado, lime wedges, and fresh salsa, letting diners assemble their own tacos.