Spray the bottom of a medium sized saucepan / casserole dish 5 times with the cooking spray.
Turn the heat on high under the saucepan / casserole dish then when the oil begins to bubble turn down the heat to medium.
Add the onions and garlic and stir these constantly together until soft about 5 minutes and use drops of hot water if they begin to stick to the bottom of the pan.
Add the green chilli paste, ground cumin, ground turmeric, chilli powder and ground ginger and stir the spices into the mixture for approximately 2 minutes. Turn off the heat and allow to cool a little.
Remove the spiced onion mixture to a blender and puree to a sauce consistency.
Add the sauce back to the pan and bring back to a simmer. Then add the cubed lamb and the warm water. Stir the mixture together until combined then put on the lid and cook for approximately 1 hour – 1 hour 30 minutes until the lamb is cooked and tender.
Stir in the tamarind pulp and cook for a further 5 minutes.
Serve on rice garnished with coriander. (Rice not included in Nutrition Label calculation)
Notes
You could substitute the Lamb for Beef. I've tried both and both work equally well.