Slice the fish into manageable pieces if needed. Coat each fillet generously with blackening seasoning. Let it sit for about 30 minutes so the spices can soak in and flavor the fish all the way through.
While the fish marinates, shred the cabbage, prepare your pico de gallo, and whisk together the sauce with mayonnaise, sour cream, lime juice, and a pinch of seasoning. Set everything aside so assembly is quick and easy later.
Heat a nonstick skillet over medium-high heat. Melt the butter until it foams, then add the fish. Cook each side for about 3–4 minutes until the crust is darkened but not burnt. Flip gently so the fish stays intact and flaky.
Heat tortillas in a dry skillet or directly over a flame until soft and lightly toasted. This makes them more flavorful and less likely to tear when filled.
Flake the fish into bite-sized pieces and place them in the warm tortillas. Top with shredded cabbage, pico de gallo, and a drizzle of the creamy sauce. Garnish with lime wedges for a final burst of freshness.