Heat the oil in a large kadhai over medium heat. Add the cumin seeds and let them crackle for 20–30 seconds.
Add the chopped onion and sauté for 5–6 minutes until golden brown at the edges.
Stir in the ginger-garlic paste and cook for 1 minute until the raw smell disappears.
Add the chopped tomatoes, turmeric, red chilli powder and coriander powder. Cook for 6–7 minutes, stirring, until the oil separates from the masala.
Add the potato cubes and cauliflower florets. Sprinkle in the salt and mix well so every piece is coated in masala.
Pour in the water, cover with a lid and cook on low-medium heat for 12–15 minutes, stirring once halfway, until the vegetables are tender.
Sprinkle garam masala over the top, mix gently and cook uncovered for 2 minutes.
Garnish with fresh coriander leaves and serve hot with roti, paratha or rice.