Pat mahi mahi fillets dry with paper towels. If fillets are large, cut into four sandwich-sized portions (about 4–5 ounces each). Season both sides evenly with kosher salt and black pepper.

Coat with blackening spice

Sprinkle the blackening spice mix over both sides of each fillet, pressing gently so the spice adheres and forms an even coating.

Cook fish

Heat a large cast-iron skillet or heavy sauté pan over medium-high heat until very hot. Add the neutral oil and swirl. Add 1 tablespoon butter, then place fillets in the pan. Cook undisturbed for 2–3 minutes until a dark crust forms. Flip carefully and add remaining tablespoon butter; cook 2–3 more minutes until fish reaches an internal temperature of 130–140°F (it will continue to cook slightly). Total cook time will vary by thickness (approx. 4–7 minutes). Transfer to a plate and let rest 2 minutes.

Mango Slaw

Combine produce

In a mixing bowl combine julienned mango, shredded cabbage, sliced red bell pepper, sliced red onion, and chopped cilantro.

Make dressing & toss

Whisk together lime juice, rice vinegar, honey, extra-virgin olive oil, kosher salt, and black pepper in a small bowl. Pour the dressing over the mango-cabbage mixture and toss until evenly coated. Taste and adjust seasoning with additional salt or lime juice if needed. Refrigerate while you cook the fish for flavors to meld (at least 10 minutes).

Garlic Herb Aioli

Mix aioli

In a small bowl combine mayonnaise, minced garlic, lemon juice, Dijon mustard, chopped parsley, chopped chives, salt, and black pepper. Stir until smooth. Refrigerate until ready to assemble so flavors meld (15 minutes recommended).

Assembly & Finish

Toast buns

Split the rolls or brioche buns and butter the cut sides lightly. Toast cut-side down in a clean skillet over medium heat until golden and crisp, about 1–2 minutes.

Build sandwiches

Spread about 1 tablespoon garlic herb aioli on each bottom bun. Place a handful of baby arugula or lettuce if using. Lay a blackened mahi fillet on top, then spoon a generous 1/4 to 1/3 cup of mango slaw over the fish. Finish with more aioli on the top bun if desired and close the sandwich.

Serve

Serve immediately with lime wedges on the side for squeezing. Leftover aioli and slaw can be kept refrigerated for up to 2 days; cooked fish is best eaten same day.