Preheat oven to 400F. Spray a roasting pan several times to coat with the vegetable oil. Put the mustard, paprika, cumin, chili powder, and cayenne pepper in a large bowl. Wisk to blend. Prick the potatoes several times with a fork and add them to the bowl. Toss to coat the potatoes evenly. Pour the coated potatoes into the prepared roasting pan, leaving a little space between them. Bake approximately 45 to 60 minutes, until potatoes are fork tender. Serves 4.