Preheat oven to 425°. In a large pot of salted boiling water, cook potatoes until just tender, about 10 minutes. Drain.
In a large bowl, combine cooked potatoes, shrimp, corn, sausage, lemons, garlic powder, Old Bay, melted butter, and oil and season with salt and pepper. Toss until combined, then divide between two large baking sheets.
Bake until shrimp is cooked through and corn is tender, 13 to 15 minutes.
In a small bowl, whisk together mayonnaise, chives, Old Bay seasoning, Dijon, and lemon juice and zest.
Garnish dish with parsley and serve with Old Bay Mayo.
