Preheat your oven to 375 degrees and lightly grease a 9x9-inch baking dish.
Place the diced potatoes in the dish, spreading them out evenly in a single layer. Bake for 15 minutes, until the potatoes are tender but not yet browned. Top with the nuggets, arranged so that none of the pieces are overlapping. Return the pan to the oven and bake for another 10 minutes. The nuggets should be golden and gently crisped.
Pour the buffalo sauce all over, as evenly as possible, and bake for another 5 minutes. Finally, sprinkle the vegan cheese on top and bake for 10 minutes longer, until melted, bubbly, and lightly browned.Finish with a sprinkle of fresh scallions on top and serve immediately.
Notes: To make your own buffalo sauce from scratch, whisk together ½ cup melted vegan butter, 2/3 cup hot sauce, 2 tablespoons apple cider vinegar, and ½ teaspoon soy sauce. If you want it even spicier, add cayenne pepper, to taste.