In a bowl toss potatoes with evoo, salt, and pepper until completely coated. Place on a large baking sheet and bake until fork tender, about 60 minutes.
Remove from oven and allow cool at room temperature for an hour or so, then place in fridge overnight to cool completely.
The next day, cut the potatoes into wedges, toss with more evoo and zaatar and bake at 375°F for at least 45 minutes, until golden and crispy. Serve with scallion sauce.
Scallion Garlic Sauce
Stir together mayonnaise, scallions, lemon zest, and garlic in a bowl. Season with salt and pepper.
Chill 2 hours or up to 3 days. Serve with roast potatoes.