Heat the oil in a pan and quickly fry the onion for 2 minutes. Add in the diced pumpkin and cook for a minute before adding in the curry paste. Again, cook the curry paste for a minute to release its flavours, then add in the lemon grass, cardamom, cinnamon stick, lentils and stock. Mix well, bring to the boil then reduce the heat to a simmer. Cook gently for 15-20 minutes, or until both the lentils and pumpkin are soft and cooked. Meanwhile, mix all the ingredients together for the bhajis so that the mixture holds its shape. Shape into mounds using 2 tbsp and cook in hot oil till golden and crispy. Stir the chickpeas and chopped herbs into the cooked curry and serve the curry into bowls. Drizzle the yogurt over the top and serve with the cooked rice or warm naan bread and the onion bhajis on the side.