Place red onion in a bowl, cover with cold water, and let sit.
STEP 2
In a large bowl, combine paprika, coriander, cumin, smoked paprika, cayenne, mustard, cardamom, and 1 teaspoon salt. Stir in oil, tomato paste, garlic, and ginger. Add cauliflower, toss to coat, then toss with chicken; let sit for 15 minutes.
STEP 3
Heat air fryer to 375°F. Pick out chicken, transfer to a second bowl, and toss with yellow onion. Air-fry cauliflower in a single layer, shaking the basket halfway through, until slightly charred and browned, about 14 minutes. Transfer to plate. Air-fry chicken mixture until cooked through, about 8 minutes. Transfer chicken to the plate.
STEP 4
Meanwhile, drain red onion, toss with lemon juice and 1/4 teaspoon salt.
STEP 5
Spread naan with yogurt; top with chicken and vegetables, then red onion, and sprinkle with cilantro if desired.