Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with aluminum foil.
Place fingerling potatoes in a large bowl. Whisk oil, mustard, dill, salt, and black pepper together in a measuring cup until well blended. Pour over potatoes and stir until evenly coated. Spread potatoes in a single layer on the prepared baking sheet.
Bake in the preheated oven for 20 minutes. Turn potatoes and cook until potatoes are golden and crispy, about 10 more minutes.