Heat oil in a pan and add the mustard seeds. When they start spluttering, add in the garlic, whole dry red chili, cumin seeds and onion.
When the onion is lightly browned, add the potato and cook covered on low heat till the potatoes are half done. (Cook on very low heat, the steam in itself will cook the potatoes. Do not add water, cooking covered on low heat helps the steam to release. Keep stirring in between to prevent burning)
When the potatoes are half cooked, add in the cauliflower florets, turmeric powder, red chilli powder and salt. Again cook on low flame till they are done. Remember to stir in between.
Finally add the methi leaves and cook for 2 to 3 more minutes before switching it off.
Serve hot with roti or rice.