01 - Preheat oven to 375°F. Line a baking sheet with parchment paper or lightly grease a baking dish.
02 - In a medium bowl, combine cream cheese, mayonnaise, egg yolk, Dijon mustard, lemon zest, Old Bay seasoning, parsley, salt, and pepper. Mix until smooth and fully incorporated.
03 - Gently fold in crab meat, chopped shrimp, celery, bell pepper, green onion, and garlic until evenly combined. Be careful not to overmix to maintain seafood texture.
04 - With a sharp knife, cut a deep pocket lengthwise into each salmon fillet, being careful not to cut all the way through. Leave about 1/4 inch intact at the bottom.
05 - Divide the seafood mixture evenly among the salmon fillets, stuffing each pocket. Mound slightly on top if necessary, using any remaining filling.
06 - Place stuffed fillets on the prepared baking sheet. Brush tops generously with melted butter to promote golden browning.
07 - Bake for 22-25 minutes, or until salmon is opaque throughout and flakes easily with a fork, and stuffing is lightly golden on top.
08 - Serve hot, garnished with additional fresh parsley and lemon wedges on the side for squeezing over the finished dish.