I dont know the english name for this kalla kai. We will usually get this in the season of Krishna Jayanthi. This will looks like Ashako tree fruit, and red and green in colour. It is sour in taste. So we will usually use this to make pickle.

Kalla kai 1/2 kg
Red chilly powder 150 gms ( you can adjust as per your taste. Oil fry red chilly and powder them)
Salt - 50 gms ( you can adjust this too)
Oil to fry

Make seasoning with mustard seeds and turmeric powder.
Crack the kalla kai to remove the white seeds from inside.
Put the cracked kalla kai in the pan and add salt, fenugreek powder and hing powder.
Mix well. Let it be for a while and stir well.
When it starts cooking add red chilly powder.
Simer the flame and when oil comes out of the pickle remove it from the fire.