Pat dry the chicken well with paper towels.
In a medium bowl, mix together Kashmiri red chili powder, salt, black pepper, ginger paste, garlic paste, vinegar, water, cornstarch, and all-purpose flour. Add chicken pieces and coat well. Allow the chicken to marinate for 10 minutes as you prep the veggies.
Preheat the air fryer for 5 minutes at 400°F. Lightly spray the bottom of the air fryer basket with oil. Line half of the chicken in the basket, ensuring not to overcrowd. Lightly spray oil over the chicken. Cook at 380°F for 10 to 12 minutes, shaking the basket halfway through. Reserve the air-fried chicken and repeat with the remaining chicken.
Heat oil in a medium skillet. Add white scallions, ginger, garlic, and green chili, and sauté for 1 to 2 minutes until the garlic starts to turn light golden and aromatic.
Then add the onions and peppers and sauté for 2 to 3 minutes. In a separate small bowl, stir together soy sauce, chili garlic paste, sugar, and water. Add this sauce to the pan and cook for 1 minute, stirring constantly.
Add the cornstarch slurry (made with 1 tbsp cornstarch and 2 tbsp water) to the pan and cook until the liquids start to thicken. Turn the heat down. Toss the air-fried chicken in the pan when you are ready to serve. Cook until everything is heated through without overcooking the onions and peppers. Garnish with scallions.
Serve immediately and enjoy your crispy chilli chicken!