Pressure cook the mustard, turnip, palak & bathua leaves with a little water, salt and turmeric. After one whistle, lower the flame and let it simmer for 30 minutes. Yes it takes a long time to cook. After 30 mins switch off the gas and wait for steam to escape fully before opening the cooker.
After opening the cooker, coarsely mash the boiled leaves with the help of a potato masher or madhani (the wooden instrument to make butter out of milk). Keep aside.
In a separate pan, heat oil and add cumin seeds and fry till they brown a little.
Add ginge and green chillies to it and fry for one minute, add onions to it and fry it slightly brown in color.
Add tomatoes and fry for about 5 mins till they start leaving oil.
At this stage, add the chilli powder and the boiled and mashed leaves. Saute for about 5-10 minutes and serve hot with makki di roti.
Note - If you don't have bathua and haven't read the whole post, I have mentioned it's substitute in the tips to make best saag section.