Summer Potato Salad SANS mayo

I was inspired by this recipe featured on Rachael Ray.  I wanted a potato salad that wasn't a mess of mayonnaise.  I roast my potatoes but this recipe calls for grilled.  Both are great options.
http://www.rachaelrayshow.com/food/recipes/team-food-grilled-potato-salad/

• 1 1/2 pounds baby red or yellow potatoes, roughly cut into chunks (pretty big chunks)
• 2 cloves garlic, smashed
• 3 to 4 sprigs thyme, leaves picked and chopped (i don't always have this on hand- use a dried herb or omit all together if you don't have fresh thyme)
• 1 lemon, half thinly sliced and half juiced, divided (i don't use the slices when roasting)
• 1/3 cup EVOO – Extra Virgin Olive Oil, divided
• Salt and black pepper
• 2 tablespoons cider vinegar
• 2 tablespoons Dijon or grainy mustard
• 3 tablespoons brown sugar
• 2 tablespoons finely chopped flat-leaf parsley
• 2 scallions, thinly sliced

Grilling Instructions: Preheat a grill to medium-heat. Scatter the potatoes in an 8-inch disposable aluminum baking tray and toss with the garlic, thyme, lemon slices, a drizzle of EVOO and some salt and pepper. Cover the tray with aluminum foil and place on the grill until the potatoes are tender, about 30 minutes if placed directly on the grill or 40 minutes if on the upper rack.
Roasting Instructions: Set your oven to 400, and either spray your baking sheet with Pam or use some tinfoil.  Drizzle some oil over the potatoes and season liberally with salt and pepper.  Roast till fork tender and nicely browned.  Turn after about 15 minutes so you get nice colour on both sides.

While the potatoes are cooking, whisk together the remaining EVOO, lemon juice, vinegar, mustard, brown sugar and parsley in a large bowl. Season with salt and pepper and toss the potatoes in while they’re still warm, giving them a good stir to evenly coat. Serve the salad warm or at room temperature, garnished with scallions.