Begin by cutting the boneless skinless chicken thighs into 1-inch pieces and placing them in a mixing bowl. Add in vegetable oil and salt, ensuring every piece is well coated. Allow the chicken to marinate for 10 minutes.

Sprinkle cornstarch over the marinated chicken pieces and use your hands or a spatula to gently toss until every piece is unevenly coated.

Preheat your air fryer to 450°F (230°C) for about 5 minutes. Once heated, place the coated chicken pieces in the air fryer basket in a single layer. Spray lightly with oil and air fry for 8 minutes, flipping halfway through.

While the chicken is cooking, mix together the ketchup, Shaoxing wine, rice vinegar, light soy sauce, brown sugar, and water in a bowl until well combined to create the sauce.

Heat a small skillet over medium heat, add a splash of oil, then add minced garlic and ginger. Sauté for about 30 seconds before adding the chopped onion and bell pepper. Cook for an additional 30 seconds.

Pour the prepared sauce mixture into the skillet with the sautéed aromatics. Stir continuously until the sauce thickens, about 2-3 minutes. Add the cooked chicken to the skillet and toss gently.

Transfer the sweet and sour chicken to a serving plate and drizzle with any extra sauce from the skillet. Serve hot as the main dish.