Heat a drizzle of oil in an oven-proof fry-pan on medium-high heat. Fry beef mince, breaking up with a wooden spoon, for about 4 minutes or until just cooked. Add nacho seasoning and fry a further 1 minute, until fragrant.
Reduce heat to low and add chilli beans, stock, tomato paste, courgette, carrots and salt. Leave to simmer for 13–15 minutes, stirring occasionally.
While mince and beans simmer, prepare the rest of the meal. Dice tomatoes 1cm; roughly chop coriander (if using); mix sour cream with sweet chilli sauce (if using), or keep plain.
Sprinkle beef mixture with cheese and place in oven for 1–2 minutes, or until cheese is melted. Top with diced tomato and coriander (if using).
Spoon nacho mixture onto plates and serve with some chips and a dollop of sour cream and sweet chilli (if using). Garnish with coriander if desired.