Steam the potatoes for 5 – 7 minutes or until they are barely tender. Set aside.
Blanch the beans in boiling water for 2 -3 minutes until barely tender. Remove from pan and plunge them into an ice water bath. Drain and set aside.
Combine the potatoes, beans, and onions in a large bowl. Add a bit of the olive oil and some salt and pepper and toss to coat everything evenly.
Spray a grill basket with non-stick spray and set on a grill over medium/high heat. Spread the potato mixture evenly in the basket.
Cook, tossing occasionally until the potatoes are golden and tender and the beans are tender with a bit of crunch. How long this will take depends on your grill. Don’t go too far away.
When the vegetables are cooked place them in a large bowl.
Combine the remaining olive oil and the rest of the ingredients in a small bowl and whisk until blended. Pour the dressing over the veggies and toss to coat. Serve warm or at room temperature.