In a large mixing bowl, combine the olive oil, marinade packet, water, and lemon juice. Stir well to blend all the ingredients.
Add the shrimp, sausage, and sliced vegetables into the bowl and mix until everything is well coated.
Prepare four pieces of 12x12 inch foil, dividing the shrimp and sausage mixture evenly among them. Fold the foil tightly, pinching the edges to ensure they are sealed.
Place the packets on a grill over medium-high heat, cooking for about 5-10 minutes on each side, or until the vegetables are tender.
Garnish with fresh parsley and a squeeze of lemon juice if desired before serving.