Dry roast the cumin seeds and dry red chilies. Allow the spices to release their aroma. Grind to a fine powder, keep aside.
Soak the poppy seeds in warm water for 15 odd minutes. Drain the water and grind to a fine paste with 2-3 green chilies. Keep aside.
Heat mustard oil in a pan, when smoking hot, add the hing, allow to splutter. Now add the parwal halves, sprinkle little salt, turmeric powder and stir fry over a medium flame till light brown.
Throw in the green mangoes, cover and cook till the mangoes are tender. 5-7 minutes I would reckon.
Stir in the posto paste, throw in the remaining green chilies, continue to stir fry till oil starts to release from the masala and the parwal are perfectly cooked. Splash a little water if it's getting a bit too dry.
Adjust seasonings and finish with a sprinkle of roasted masala. Serve hot with rice.