Melt 1 tablespoon of butter in a skillet over medium heat. Add panko breadcrumbs and toast for about 5 minutes, stirring frequently until golden brown. Transfer to a plate to cool.

In a small mixing bowl, combine mayonnaise, Sriracha, mirin, and lemon juice. Whisk together until smooth and creamy, then refrigerate.

In a medium bowl, mix crab meat and cucumber matchsticks. Pour the Sriracha mayonnaise over the mixture and stir gently to coat.

Lay shredded lettuce on a platter. Spoon crab salad mixture on top and sprinkle toasted panko breadcrumbs and sesame seeds before serving.