Cut the baby potatoes into 1-inch chunks and slice the corn on the cob into 2-inch rounds. Slice the smoked sausage into rounds, cut the yellow onion into 1/2-inch thick wedges, and mince the garlic. Cut the lemons into wedges and finely chop the fresh parsley. Having everything prepped before you start cooking ensures the assembly process is smooth and quick.
Bring a large pot of salted water to a boil and add the cut potatoes and corn rounds. Boil for 10 minutes until the potatoes are just starting to soften but still hold their shape—they'll finish cooking in the foil packets, so slightly undercooking them now prevents mushiness. Drain well in a colander and set aside.
Heat your grill or oven to 400°F. While it preheats, cut four sheets of heavy-duty aluminum foil, each about 18 inches long. I like to arrange the foil sheets on a work surface so I can easily divide ingredients among them without fumbling.
In a large bowl, combine the shrimp, sliced sausage, sautéed onion wedges, minced garlic, parboiled potatoes and corn from Step 2. In a small bowl, whisk together the melted butter with the salt, black pepper, Old Bay seasoning, smoked paprika, and Worcestershire sauce. Pour this seasoned butter mixture over the shrimp and vegetables, then toss gently but thoroughly to coat everything evenly. The Old Bay brings the signature seafood boil flavor, so make sure every piece is well-coated.
Divide the seasoned shrimp mixture evenly among the four foil sheets, placing it in the center of each sheet. Fold the foil up to create a packet, sealing the edges by crimping them tightly—make sure there are no gaps so steam stays trapped inside. Leave a little room at the top for steam to circulate and cook the shrimp gently.
Place the sealed foil packets on the preheated grill or on a baking sheet in the oven at 400°F. Cook for 15 minutes total, flipping the packets halfway through at the 7-8 minute mark to ensure even cooking. The shrimp should be opaque and cooked through, and the potatoes should be tender.
Carefully open the foil packets—watch out for steam! Squeeze fresh lemon wedges over each packet and top generously with chopped fresh parsley. Serve immediately in the foil packets for a fun, interactive meal that keeps everything hot and captures all those delicious flavors.