Place a pressure cooker on medium-high heat, add oil and diced onions. Saute until the onions become translucent.
Add cumin seeds and ginger-garlic paste and saute for 30 seconds.
Add tomatoes and the following spices - salt, turmeric powder, red chili powder, cumin powder, coriander powder. Saute for 1 minute.
Add the cauliflower and the potatoes along with 3/4 cup water. Give it a stir and close the lid of the pressure cooker.
Once the pressure develops and it starts to whistle, cook for 7 MINUTES ONLY.
Immediately turn off the heat and allow the pressure to release safely (DO NOT OPEN IMMEDIATELY).
Then open it, sprinkle garam masala and lemon juice and gently stir (taste and adjust salt if needed).
Serve hot with roti, naan or rice.