Preheat your broiler to high and position a rack about 6 inches from the heat source. Line a baking sheet or cast iron skillet with parchment paper.
Butterfly the shrimp: Lay each shrimp flat on a cutting board. Using a paring knife, cut along the back from the top to just before the tail, cutting about halfway through the shrimp. Open it flat like a book to create a small pocket.
Pat the shrimp dry on both sides with paper towels. This helps them brown instead of steam.
Make the stuffing: In a small bowl, combine the softened cream cheese, half the panko, the Parmesan, half the minced garlic, the lemon zest, Old Bay, and a pinch of salt and pepper. Mix until just combined – the mixture should be thick enough to hold a shape.
Stuff the shrimp: Spoon about 1 tablespoon of the mixture onto each butterflied shrimp, pressing gently so it stays in place. Don't overstuff.
Chill for 10 minutes in the fridge to set the stuffing so it doesn't slide off during broiling.
Make the butter drizzle: In a small bowl, combine the melted butter, remaining minced garlic, lemon juice, and a pinch of salt.
Brush or drizzle half of the garlic butter over the stuffed shrimp, then sprinkle the remaining panko on top for extra crunch.
Broil for 5-7 minutes, watching closely after 4 minutes. The shrimp should be pink and opaque, and the stuffing should be deep golden brown.
Drizzle the remaining garlic butter over the hot shrimp, sprinkle with fresh parsley, and serve immediately with lemon wedges.