Pat the mahi mahi fillets dry with paper towels. If fillets are thick, cut into 4 portions (about 4 oz each). Brush both sides lightly with 1 tablespoon olive oil and season with 1/2 tsp salt and 1/2 tsp black pepper.

Make blackening spice

In a small bowl combine 1 tsp paprika, 1 tsp garlic powder, 1/2 tsp onion powder, 1/2 tsp dried oregano, 1/2 tsp dried thyme, and 1/4 tsp cayenne pepper. Mix well and press evenly onto both sides of each fillet.

Cook fish

Heat a heavy skillet (cast iron preferred) over medium-high heat until very hot, about 3 minutes. Add 1 tablespoon unsalted butter and swirl to melt. Add fillets and sear 2-3 minutes per side until a dark crust forms and the fish is opaque and flakes easily (internal temp 137-145°F). Remove from pan and let rest 2 minutes.

Mango Slaw

Prepare mango and vegetables: Peel and dice the ripe mango into small cubes (about 1 cup). Thinly shred green and red cabbage and julienne or grate the carrot. Place mango, cabbages, carrot, red onion slices, and chopped cilantro in a medium bowl.

Make dressing: In a small bowl whisk together 1 tablespoon lime juice, 1 teaspoon honey, 1 teaspoon olive oil, 1/4 tsp salt and 1/8 tsp black pepper until combined.

Toss and chill: Pour dressing over the slaw, toss gently to coat, taste and adjust seasoning. Let sit 10 minutes at room temperature or refrigerate up to 1 hour to let flavors meld.

Garlic Herb Aioli

Mix aioli: In a small bowl combine 1/2 cup mayonnaise, 1 minced garlic clove, 1 tsp lemon juice, 1 tsp finely chopped parsley, 1 tsp finely chopped chives, 1/8 tsp salt and a pinch (1/16 tsp) black pepper. Stir until smooth. Taste and adjust lemon or salt. Chill until ready to assemble.

To Assemble

Toast buns: Heat a skillet over medium. Spread softened butter on cut sides of 4 buns or rolls and toast in skillet until golden, about 1-2 minutes per side.

Build sandwich: Spread about 1 tablespoon garlic herb aioli on the bottom bun. Place a lettuce leaf (if using), then a blackened mahi fillet. Top the fillet with 1/4 to 1/3 cup mango slaw. Spoon an extra 1 teaspoon aioli on the top bun if desired, close sandwich.

Serve: Serve immediately with lime wedges for squeezing over the fish and additional mango slaw on the side.