Preheat: Set oven to 375°F (190°C). Line a baking sheet with parchment paper.
Make Filling: In a large bowl, combine the shrimp, crab meat, cheddar, cream cheese, mayo, Dijon, Old Bay, garlic powder, and pepper. Mix until evenly distributed.
Prep Biscuits: Separate the biscuit dough. On a floured surface, flatten each biscuit into a round disc about ¼ inch thick.
Fill: Place a generous spoonful of the seafood mixture in the center of each disc.
Seal: Fold the dough over the filling to create a half-moon shape. Pinch the edges tightly to ensure the seafood doesn't leak during baking.
Brush: Arrange on the baking sheet and brush the tops with melted butter.
Bake: Bake for 15–20 minutes until the biscuits are puffed and golden brown.
Finish: Let cool slightly, garnish with fresh parsley, and serve warm.