Heat oil in a heavy medium sized saucepan and add the sliced garlic and ginger. Saute for a minute till the garlic gets light golden and aroma is released.
Add the chopped onion, and saute for 2 – 3 minutes till onion is translucent.
Add the whole spices (cumin seeds, black peppercorn, cinnamon stick and cloves) and saute for a minute.
Add the powdered spices (coriander powder, red chili powder, turmeric powder and curry powder) and saute for around 2 minutes. In case the spices stick to the bottom of the pan, add a splash of water.
Add the cubed carrot, potato and apple and saute for a minute. Then add the soaked lentils, followed by the vegetable stock.
Bring the soup to a boil, and then turn heat to low.
Partially cover with a lid and cook for around 30 minutes till vegetables and lentils are tender and soft.
Turn off the heat, and remove the whole spices, especially the cinnamon stick and the cloves.
Blend with an immersion blender, till smooth or let it cool for 10 – 15 minutes and then blend it in batches in a blender.
Turn heat to medium, and bring the soup to a light bowl. Add salt, and lemon juice. If preferred additional liquid can be added at this stage.
Garnish with coriander leaves, and serve hot with boiled rice and yoghurt on the side.