Put the cumin seed and mustard seed in a small heavy bottomed pan and roast over heat until the spices are fragrant, but be careful not to burn them. The key is to keep the spices constantly moving in the pan by shaking it with a swirling motion.
Put the spices in a spice grinder and pulverize.
Add everything including the toasted spices into a blender and blitz until smooth. Add some water if the chutney is too thick then adjust salt to taste.
Stored in an airtight container in the fridge your green chutney should last at least 1 week.