Bring a large pan of water to the boil, add the spinach and cook for 2 minutes. Drain, then run under cold water to cool. Squeeze out the excess water, roughly chop and set aside.
Heat a large pan or wok over a medium-high heat and add the balti paste. Allow to sizzle for a minute, then add the aubergine and stir-fry for 7-10 minutes.
Add the chopped tomatoes, vegetable stock and lentils. Reduce the heat and simmer for 10 minutes.
Stir in the chopped coriander, spinach, leftover cauliflower and cabbage, then simmer for a further 5 minutes until the lentils are tender and the veg are piping hot. Garnish with the reserved coriander leaves and serve with the flatbreads.