Preheat the oven to 400°F or prepare your grill for medium-high heat.
In a large bowl, combine the shrimp, baby potatoes, and corn.
Drizzle the olive oil over the mixture and sprinkle with Cajun seasoning, garlic powder, onion powder, smoked paprika, salt, and black pepper. Toss everything together until well coated.
Cut four large pieces of aluminum foil (about 12x18 inches each).
Divide the shrimp and vegetable mixture evenly among the foil pieces, placing them in the center.
Top each portion with lemon slices.
Fold the sides of the foil over the mixture and seal tightly to create packets.
Place the packets on a baking sheet if using the oven or directly on the grill.
Bake in the oven for 20-25 minutes or grill for 15-20 minutes, until the shrimp are cooked through and the potatoes are tender.
Carefully open the packets (steam will escape) and garnish with fresh parsley before serving.