Preheat the oven to 180°C, fan 160°C, gas 4. In a large frying pan, heat the oil and add the peppers, courgettes and onion. Gently stir-fry for 5 minutes until tender.
Add the cooking sauce and lentils; bring to a simmer and cook for 5 minutes until the vegetables are tender (add a little boiling water if it's too thick). Meanwhile, put the naan breads on a baking tray and warm in the oven for 5 minutes.
Divide the curry between 4 bowls. Garnish with the mint and serve each with half a naan.