In a medium bowl, combine prawns and 1 tablespoon old bay seasoning. Let it sit for 5 minutes.
Meanwhile, in a large bowl, combine corn, baby potatoes, sausage, lemon and garlic. Add in the seasoned shrimp. Add 2 tablespoons melted butter, 1 teaspoon parsley, and remaining tablespoon of old bay seasoning. Toss together and let it sit for 10 minutes.
You can grill these on either a grill pan or an outdoor barbecue grill.
To cook on a grill pan: Brush grill with olive oil and heat on medium-high heat. Add items on the grill, and gently brush the remaining butter on top. Grill for 5 minutes until you see some distinct grill marks. Then, reduce heat to medium, flip the items over, and add 1 cup of water. Cover with aluminium foil and simmer for 15 minutes.
To cook on barbecue grill: Brush grill with olive oil or spray with cooking spray. Add items on the grill, and grill for a few minutes until you see some distinct grill marks. Remove items from the grill, and place into a large disposable aluminum tin, add in remaining butter, and cover with aluminum foil and seal the edges (OR divide onto four 12-inch sheets of aluminum foil. Divide the remaining butter amongst them. Fold over to create a pocket and seal the edges by rolling them up). Place aluminum pan or foil packets on the grill and cook for 15-20 minutes until cooked through.
Serve with remaining chopped parsley on top and Old Bay seasoning.