Heat two tablespoons of vegetable oil in a large lidded saucepan over a medium heat. Add the red onion, aubergine and garam masala and fry until starting to brown, about 8-10 minutes.
Dry fry the cumin and coriander seeds in a small frying pan until fragrant, then add to the onion mixture and stir well.
Add the remaining ingredients, stirring well to combine, then cover the pan with a lid.
Bring the mixture to a simmer and cook for 15-20 minutes, stirring occasionally, until the cauliflower florets are tender. Season, to taste, with salt and freshly ground black pepper.