Preheat the oven to 425°F (220°C) and line a baking sheet with parchment paper.
In a large bowl, combine the flour, baking powder, garlic powder, onion powder, and salt. Add the cold, cubed butter and use a pastry cutter or your fingers to work the butter into the flour until the mixture resembles coarse crumbs.
Stir in the shredded cheddar cheese and chopped parsley.
Gradually add the milk, mixing until just combined. Do not overwork the dough.
On a lightly floured surface, roll the dough into a ½-inch thick sheet. Use a round cutter to cut out 12 biscuits.
To prepare the crab filling, gently mix the crab meat, mayonnaise, Dijon mustard, lemon juice, Old Bay seasoning (if using), and parsley in a bowl.
Take one biscuit and gently create a pocket in the center. Spoon in about a tablespoon of the crab mixture and seal the biscuit around the filling. Repeat with the remaining biscuits.
Place the stuffed biscuits on the prepared baking sheet and bake for 15-20 minutes, or until the biscuits are golden brown.
While the biscuits bake, prepare the lemon butter by combining melted butter, lemon juice, lemon zest, and parsley in a small bowl.
Once the biscuits are done, remove them from the oven and immediately brush the lemon butter over the top of each biscuit.
Serve warm and enjoy these flavorful, crab-filled cheddar biscuits!