Preheat your grill or a grill pan over medium-high heat and lightly brush the grates with oil to prevent sticking.
In a small bowl, whisk together the miso paste, soy sauce, maple syrup, rice vinegar, sesame oil, and a pinch of salt until you have a smooth, glossy glaze.
Parboil or microwave the potato wedges for 4–6 minutes until they are just tender but still hold their shape. This helps ensure the centers cook through without burning the glaze.
Pat the wedges dry with a clean towel. Toss them with a little neutral oil and a pinch of salt to prevent sticking on the grill.
Brush the miso glaze generously over all sides of the potato wedges. Let them sit for 2–3 minutes to absorb some flavor.
Grill the wedges in a single layer, turning occasionally and brushing with more glaze, until the outsides are caramelized and slightly charred and the centers are tender, about 8–12 minutes total.
Transfer to a platter. Drizzle with any remaining glaze, then sprinkle with toasted sesame seeds and sliced scallions.
Serve warm as a side dish or as a hearty vegetarian main with a grain base like quinoa or brown rice.