Preheat oven to 425°F (220°C). Line a large rimmed sheet pan with parchment paper or grease with non-stick spray.
Place halved potatoes in a large pot of salted water. Bring to a boil and cook for 8 minutes. Add corn pieces for the final 2 minutes of boiling. Drain well.
In a small bowl, whisk together melted butter, minced garlic, Old Bay seasoning, smoked paprika, salt, and pepper.
In a large mixing bowl, combine the parboiled potatoes, corn, sliced sausage, and raw shrimp.
Pour the butter mixture over the ingredients and toss until everything is thoroughly and evenly coated.
Spread the mixture onto the prepared sheet pan in a single even layer. Tuck lemon slices between the ingredients.
Roast for 12 to 15 minutes, or until the shrimp are pink and opaque and the corn is tender.
Remove from oven and garnish with fresh chopped parsley. Serve hot.