In a large pot, bring the water to a boil and add the Old Bay seasoning.
Add the fish fillets to the boiling water and cook for about 5-7 minutes, or until the fish is opaque and flakes easily with a fork. Remove the fish and let it cool slightly.
In a bowl, combine the butter, lemon juice, mayonnaise, Dijon mustard, garlic powder, salt, and pepper. Mix well until smooth.
Flake the cooked fish into bite-sized pieces and gently fold it into the mayonnaise mixture until well coated.
Toast the hot dog buns lightly on a skillet or in the oven until golden brown.
Place a layer of shredded lettuce in each bun and generously fill with the fish mixture.
Serve immediately with lemon wedges on the side.