1. To make the remoulade, whisk mayonnaise, scallions, relish, lemon juice, mustard, and hot sauce in a small bowl until combined; cover and refrigerate until ready to serve.
2. Heat grill to high for at least 10 minutes, then clean and generously oil grates. Meanwhile, whisk paprika, onion powder, garlic powder, cayenne (if using), 1/2 teaspoon salt, and 1/2 teaspoon pepper in a small bowl. Rub mixture all over fish, then cover and refrigerate until ready to grill. Spread butter over inside of rolls.
3. Lightly pat fish dry with paper towels (this will prevent sticking), then grill, flipping once, until fillets flake easily and are opaque throughout, about 4 minutes per side. Transfer fish to a clean plate and cover loosely with foil to keep warm. Grill buttered side of buns until lightly browned, about 1 minute.
4. To serve, spread remoulade evenly over bun bottoms, then top with fish, lettuce, onion, and tomato. Top with remaining bun halves and serve.
Source: Hannaford fresh Magazine, May - June 2020