How to Make It
Stir together ketchup, chili sauce, horseradish, lemon zest, lemon juice, Old Bay seasoning, and hot sauce in a medium bowl; chill until ready to use.
Preheat oven to 450°F. Place butter, garlic, lemon slices, and crushed red pepper in the center of a rimmed baking sheet. Place baking sheet in oven, and heat until butter melts and garlic is fragrant, about 5 minutes.
Add shrimp, and toss in butter mixture; spread in a single layer. Roast in preheated oven until shrimp turn pink and are just cooked through, 4 to 5 minutes. Transfer shrimp and pan juices to a large platter.
Squeeze juice from roasted lemon slices over shrimp; sprinkle with fresh parsley, salt, and pepper. Serve with chilled cocktail sauce.