To make the salsa, toss all the ingredients together with a pinch of salt.
To make the yogurt sauce, mix all the ingredients with a pinch of salt.
Heat the oven to 200C/fan 180C/gas 6. Rinse the chickpeas in a sieve under running water then drain well and pat dry on kitchen paper. Toss the chickpeas with the oil and ½ tsp of salt, and spread out on a baking tray. Cook for 30-35 minutes or until golden and crisp on the outside. Toss with the cumin seeds and curry powder, and cook for another 2-3 minutes.
Brush the naan pieces with melted butter and spread out on a baking tray. Cook for 15 minutes until crisp, then cool.
To assemble the nachos, spread the crispy naan pieces over the base of a heatproof serving dish. Scatter over the cheese, chilli and ½ the chickpeas, and put back in the oven for 5 minutes until the cheese has melted.
Top with the remaining crispy chickpeas, scatter over the salsa and drizzle with the yogurt sauce.