In a mixing bowl, combine the mayonnaise, minced capers, and fresh lemon juice. Stir until well mixed.
Pat the salmon fillets dry with a paper towel. Sprinkle ½ teaspoon of kosher salt evenly over the salmon pieces.
Take the beaten egg whites and dip each salmon piece into the egg, ensuring it’s fully coated. Roll the salmon in the seasoned panko breadcrumbs, pressing gently to adhere the crumbs to the fish.
Preheat your air fryer to 400°F (200°C). Lightly spray the air fryer basket with olive oil spray. Place the breaded salmon pieces in the basket in a single layer. Cook for about 10-12 minutes, flipping halfway through, or until golden brown.
While the salmon is cooking, toast the whole wheat buns. Spread a generous amount of the caper mayonnaise on the bottom half of each bun. Place a piece of crispy salmon on top, followed by a butter lettuce leaf, and finish with the top half of the bun.
Serve your Air Fryer Salmon Fish Sandwich with a side of fries or a simple salad for a complete meal.