Preheat oven to 425-degrees. Line a large rimmed baking sheet with parchment.
Toss potatoes with oil; season with salt and pepper. Arrange on baking pan; roast 20-25 minutes, or until golden brown and tender.
Meanwhile, melt butter in medium saucepan over medium-high heat. Add onions; sauté 2 minutes. Stir in garlic powder, broth, and beef base. Mix cornstarch with 3 tablespoons water until well blended.
Bring broth mixture to a boil; whisk in the cornstarch mixture, stirring constantly until gravy is thickened. Season with salt and pepper.
Serve hot potatoes in shallow bowls, topped with cheese curds and a spoonful of gravy, sprinkled with green onions.