Heat oven to 425. Cut the yams lengthwise into 4 wedges per yam. Put them in a large bowl, and toss them with the honey, ½ tablespoon of the Espelette pepper or crushed red-pepper flakes and 2 tablespoons of the olive oil. Let it sit for 10 minutes or so, tossing once or twice to coat, as the oven heats.
Transfer the yams to a foil-lined, rimmed baking sheet, season with salt and pepper and then bake until they are deeply caramelized around the edges and soft when pierced with a fork at their thickest part, approximately 30 to 35 minutes.
As the yams roast, combine the yogurt, lime juice and remaining tablespoon of olive oil in a small bowl, and whisk to combine, then season with salt and pepper to taste. Set aside.
When the yams are done, transfer them to a serving platter, drizzle the yogurt over them and garnish with the remaining Espelette pepper or red-pepper flakes, the scallions and some flaky sea salt if you have any.