Fry the onion in the oil for 2-3 minutes or until just tender. Add the potatoes and fry for 2-3 minutes.
Add the cauliflower, stir and fry for 4-5 minutes. Add the green chillies, coriander, ginger, and salt. Mix well.
Cover and cook for 5-6 minutes on a low heat, or until the potatoes are tender.
Sprinkle with lemon juice and garam masala before serving.