If you haven't cooked your lentils, cook them now. You want two cups cooked for the soup.
Heat a water in a saucepan and bring it to boil. Chop the red potatoes into a little bigger than bite size and add them to the water. Boil for about 10 minutes, until tender.
Chop the veggies. Slice the garlic, shallots and leek. Thinly slice the onion and celery.
Heat a large soup pot on medium heat. Once hot, add the oil. Add the cumin seeds and cook for about 30 seconds to a minute, just until fragrant. Add the garlic and cook until fragrant and just golden. Add the shallots and leek and cook until translucent, about 1-2 minutes.
Add the vegetable stock and water. Bring to a boil and reduce to a simmer. Let it simmer for 10 minutes. The potatoes should be done by now, add those to the soup with the cumin and coriander. Cook for 10 minutes to let the flavors develop. Add the lentils, lime juice, garam masala, salt and pepper (we added about 1/2 teaspoon each of s&p) and a sprinkle of cayenne if you like heat.
Let it simmer for as long as you want to continue developing flavors, or you can serve now. Top with cilantro and green onions if desired and enjoy!