In a pressure cooker add cleaned and chopped greens along ginger & green chillies. Boil for one whistle and then 5 minutes on low flame. Set aside till the steam releases and cool the greens. Once the greens are slightly cool, grind them coarsely using a mixie.
In a heavy bottom kadai (I love to do this in a cast iron pan), heat mustard oil and add onions. Sautee till they turn brown. Add tomatoes and sautee till they are soft and the oil seperates.
Add salt, chicken and fry till the masala coats the chicken and chicken starts to change color slightly. Add the puree greens and cook till the chicken is tender and the gravy thickish.
Now in a small tadka pan, heat the mustard oil and add jeera. Fry till it is brown, add chilli powder and garam masala. Pour over the chicken, garnish with chopped raw ginger and serve hot.
PS - If you don't have the exact greens handy, you can mix it up with what you have at home. I have made this many different greens in various ratios and it has always come out well.