With paper towels, pat the chicken legs dry, and place in a large mixing bowl. Drizzle with the oil.
In a small bowl, stir together the brown sugar, smoked paprika, salt, pepper, mustard, and cayenne. Sprinkle over the chicken, then toss to evenly coat.
Preheat the air fryer to 400 degrees F, according to the manufacturer’s instructions. Arrange a single layer of the drumsticks in the basket.
Air fry chicken legs for 10 minutes, then slide out the basket and flip the legs. Return to the air fryer and cook for 8 additional minutes, until the chicken reaches at least 165 degrees F when a meat thermometer is inserted at the thickest part without touching the bone (I remove mine around 190 degrees F and it is still very juicy. The extra time ensures the skin is nice and crisp). Transfer to a plate and let rest 5 minutes. Serve hot, sprinkled with chopped cilantro or parsley as desired.
TO STORE: Refrigerate chicken in an airtight storage container for up to 4 days.
TO REHEAT: Gently rewarm leftovers on a baking sheet in the oven at 350 degrees F or in the microwave.
TO FREEZE: Freeze chicken in an airtight, freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.