Heat oil in a pan and add the chopped onions. When the onions turn soft, add the ginger and garlic and saute until fragrant (about 2 mins).
Add the potatoes and cauliflower to this and cook on lowest heat, covered, mixing now and then so the vegetable pieces don't burn.
When the vegetables are half cooked, add the tomato paste and mix again. Cook again for 3-4 mins or until the vegetables are soft (not mushy).
Add the spice powders - coriander powder, turmeric powder, jeera powder, and chilli powder. Mix again until well combined. Cook until the spice powders don't smell raw anymore - another 2 mins or so. The potatoes and cauliflower should be roasted and dry by now. Add salt.
Finish off with a generous amount of chopped coriander leaves and mix again.