In a dry skillet, roast together 2 tablespoons of cumin seeds and 1 teaspoon of Sichuan red peppers if using until fragrant. When they have cooled, use a mortar and pestle and give them a rough grind.
Use a fork to poke holes into the lamb to allow the marinade to penetrate better.
In a large bowl or a Ziploc bag, marinate the lamb with the cumin and Sichuan pepper blend, oil, soy sauce, garlic, red chili peppers, salt, sugar and cayenne pepper (if using).
Set your air fryer to 360F for 10 minutes and place the marinated lamb in a single layer in the air fryer basket.
Using a meat thermometer, ensure that the lamb has reached an internal temperature of 145F and remove to a serving tray.
Mix in the chopped scallions and cilantro, and serve.