Cut potatoes into large bite-size pieces. Mix generously with black bean chili oil and salt and spread out evenly on a baking sheet.
Back at 400°F for 15 minutes, then stir to make sure potatoes aren't sticking to pan. Lower oven temperature to 375°F (190°C) and bake for another 25 to 30 minutes, stirring once, until lightly browned and crispy.
Remove to a bowl and stir in more black bean chili oil to taste before serving.
Substitute cauliflower for an equally delicious dish using the exact same procedure.