In a large bowl, combine the vindaloo spice mix, garlic and ginger paste, tomato paste, yogurt, vinegar, and a pinch of salt. Mix until smooth.
Add the chicken thighs or breasts to the marinade, ensuring each piece is thoroughly coated. Let it marinate for at least 30 minutes, or overnight for deeper flavor.
Set your air fryer to 375°F (190°C) and let it preheat for about 3 minutes.
Place the marinated chicken in a single layer in the air fryer basket. Brush or spray with a little oil to prevent sticking. Cook for 12-15 minutes, flipping halfway through, until the chicken reaches an internal temperature of 165°F (74°C).
While the chicken cooks, sauté onions in a small pan until golden, then add leftover marinade and simmer until thickened.
Plate the chicken with the sauce, garnish with fresh cilantro, and serve alongside rice or naan for a complete meal.