Place fish cubes in a bowl. Add ginger-garlic paste, green chilli paste, lemon juice and salt. Mix well and set aside to marinate for 20 minutes.
Heat mustard oil in a non-stick pan, add carom seeds, garlic, green chillies and sauté till the garlic becomes golden.
Add gram flour, reduce heat and sauté for 1-2 minutes. Transfer into a bowl. Add red chilli powder, turmeric powder, garam masala powder, black salt, yogurt and little water and mix. Add the marinated fish and salt and mix well. Set aside to marinate for
Grease the basket of the air fryer with a little oil. Place the marinated fish pieces on the base. Cook on barbecue mode in the air fryer at 200° C for 8-10 minutes or till done. Transfer onto a serving plate and serve hot.