Heat 2 tbsps of oil in a deep saucepan. When hot add the onion and fry until soft and translucent, but not golden. Now add the garlic, ginger and green chillies and stir for a couple of minutes.
Add the peas, hot stock, lemon juice and garam masala and bring to the boil. Add the herbs and stir to mix, then remove from the heat. Allow to cool slightly then whizz in a blender. Pour back into the pan and gently reheat.
Meanwhile make the cumin flavoured oil to pour over the soup. Pour a slug of oil into a small frying pan over a medium heat and when hot add the cumin seeds. Leave to sizzle until they brown, add the salt and take off the heat.
Divide the soup between four bowls , sprinkle over the remaining mint leaves and pour over the cumin oil.