If using mustard oil to coat the cauliflower and potatoes, heat a wok/kadhai or a wide saute or frying pan on medium heat and add half the oil. Let the oil heat, and then add cauliflower florets and sliced potatoes. If you are not using mustard oil, just place the cauliflower and potatoes in a wide bowl or directly on a sheet pan (if roasting them).
Sprinkle half of the salt and turmeric powder, stirring to coat them well with the oil and spices.
To roast the seasoned cauliflower florets and potatoes in an air fryer, transfer them to the air fryer basket. Roast at 350 for 8-10 minutes, then flip the charred pieces again and roast for 6-8 minutes more.
Alternatively, to roast the seasoned cauliflower florets and potatoes in the oven, spread in a single layer on a lined baking sheet and roast for 15-20 minutes at 400°F. Check for desired tenderness.
While the cauliflower and potatoes are roasting, heat the rest of the oil in the same pan, add asafetida, cumin seeds, ginger and green chilis. Sauté for few seconds.
Add nuts and seeds and let it roast for few seconds.
Now add chopped tomato and saute it until soft and mushy.
Keep stirring intermittently for even cooking and add the remaining salt and turmeric powder.
Cover with a lid to expedite the cooking process; it will take roughly 10 minutes to cook tomatoes.
Now add roasted cauliflower florets and potatoes to the cooked tomato masala.
Add all the spices and mix well.
Let the whole mixture cook for 5 minutes so that all the spices get amalgamated into each other.
Finish with a sprinkle of garam masala and amchur powder.
Garnish with chopped cilantro, and enjoy.
The whole dish needs to be cooked on medium heat.