Preheat the oven to 425°F. and spray a large, rimmed baking sheet with nonstick spray.
In a large bowl, toss the yams with butter. Spread in a single layer on the prepared baking sheet. Roast until tender, about 20 to 25 minutes, tossing the yams to rearrange midway through baking.
Meanwhile, prepare the glaze. In a small saucepan, combine the orange juice, brown sugar, salt and ginger. Bring to a boil, stirring occasionally. Reduce heat and cook, until mixture is syrupy and reduced by about a third (about 5 minutes).
Brush the roasted yams with the glaze. Carefully scoop the yams into to a 9x13-inch casserole dish. (Make ahead tip: At this point you can cover with plastic wrap and refrigerate until you're ready to serve. Bring them to room temperature, then microwave them until hot and continue with the recipe).
Sprinkle the marshmallows on top and place the dish under a broiler until the marshmallows are warm, toasted and gooey. Keep an eye on it so you don't burn the marshmallows!
Notes
If you are preparing this recipe as gluten free, just make sure that you use gluten-free marshmallows.