Meanwhile, place potatoes and lemon, cut side down, on the grill or grill pan and cook until potatoes are lightly browned and crisped, about 5 minutes per side, and lemon has blackened on the cut side. Transfer potatoes to a large bowl and squeeze the grilled lemon halves over the potatoes. Gently toss to coat. Let stand while sausages and vegetables finish cooking.
Put peppers and onions on the grill, and cook, turning occasionally, until they are softened and dark in spots, 5 to 8 minutes. Transfer to a cutting board and chop coarsely. Add the chopped vegetables to the bowl with the potatoes.
In a small bowl, whisk together both mustards, remaining 2 tablespoons oil, remaining 1/2 teaspoon salt, pepper and parsley. Drizzle over the potatoes and vegetables and toss to coat. Garnish with more parsley, if desired.
Place the sausages on the hot side of the grill and cook, turning once until they are browned on both sides, about 3 to 5 minutes. Transfer to a platter. Serve the sausages with the potato salad.
Nutrition information per serving:
Calories700Fat48 gSodium1,770 mg