Grilled Lemon Potato Salad

2 lbs small yukon gold or red potatoes, or larger and cut into 1/4s
1 large lemon, cut in half
1/2 cup olive oil
2 teaspoons grainy mustard
1/2 vidalia onion, diced small
1/4 cup chopped fresh chives
salt and pepper

1. Place unpeeled potatoes in a large pot with enough water to cover by 1 inch. Add 1 teaspoon of salt. Bring to a boil over medium-high heat and cook until potatoes are just tender, 15 to 20 minutes depending on size. Drain and let cool. Cut small potatoes in half or quartered potatoes in half again. Add to a bowl and gently toss with olive oil until coated. Season with salt and pepper and toss again. Coat the cut halves of the lemon with olive oil.
2. Heat a grill to medium-high. Place the potato chunks on the grill and cook until grill marked on most sides. Grill the lemon cut side down until grill marked and slightly charred.
3. Add the potatoes back into the same bowl and squeeze the grilled juice lemon over the potatoes. Drizzle with a little more olive oil and add in the mustard. Add the diced onion and chives and season with additional salt and pepper. Toss until mixed. Serve immediately.