Place the potatoes in a large saucepan. Cover with cold water, set over high heat and bring to a boil. Boil until the potatoes are just tender when pierced with a fork 15 to 18 minutes. Drain and let rest until cool enough to handle.
Cut the potatoes in half lengthwise. Place the potatoes in a bowl and toss with the olive oil, salt and pepper.
Preheat the grill to medium-high. Lightly brush the grill with oil. Pierce the sausages in a few places. Cook on the grill until browned and heated through, turning occasionally, 7 to 10 minutes. Transfer to a cutting board and cut each sausage into 6 pieces.
Grill the potatoes until they have golden brown grill marks, 3 to 4 minutes per side.
Using 4 plates, divide the spring lettuce mix, sausages, potatoes and tomatoes between the 4 plates.
Drizzle each salad with 2 teaspoons dressing. Serve.
In a small bowl, whisk together the balsamic vinegar, Dijon mustard, agave nectar and salt. While whisking, slowly pour in the olive oil.