Rinse the lentils several times until the water is clear. Transfer the lentils to a small saucepan.
Add 3 cups of vegetable stock. Over medium heat, bring the lentils to a simmer and cook for 15 minutes until the lentils are tender the stock has been absorbed.
In a large soup pot, heat the 2 Tablespoons canola oil over medium high heat. Add the ginger and garlic paste and cook for 1 minute. Add the onion and saute for 2 - 3 minutes, being careful not to brown the onion. Add the chile and spices and cook for another two the three minutes until the spices are fragrant.
Reduce the heat to medium low, cover the pan and cook for 10 - 15 minutes, stirring occasionally until the onions are tender.
Add the canned tomatoes, remaining 3 cups vegetable stock and lentils. Stir to combine.
Increase the heat to medium high and bring the soup to a simmer. Cover the pot and simmer for 10 minutes to allow all the flavors to blend.
** for the ginger garlic paste, you can purchase ginger garlic paste in indian markets or buy individual containers of ginger paste and garlic paste in your local supermarket. But the easiest thing to do is to add ¼ cup peeled, chopped ginger and ¼ cup peeled garlic cloves to a small food processor and process until a paste is formed. Paste will keep about 4 -5 days in the refrigerator.
Notes:The keys to making this soup are to cook the lentils separately in the stock! Yes, I know it's an extra step, but the difference is worth it. The lentils aren't over cooked!!! This soup is on the thinner side. If you like a thicker, chunkier soup, reduce the added vegetable stock by 1 to 1 ½ cups. Since chiles differ in how hot they are, I usually start with about ½ of a chile. After sauteing the onions and spices (with the chile!) I give it a little taste. If you think it needs more chile, add a bit more. Definitely easier to add more than to try and make it milder! This Indian lentil soup makes a terrific dinner or lunch. Serve with a side of rice or naan bread and a salad or vegetable side dish. You can definitely freeze this soup - it reheats beautifully!