Heat the oil in a large saucepan (you can also use a mix of vegan "butter" like Earth Balance and oil)
Add the onion and saute for a few minutes until it becomes translucent. Add the sugar and continue to saute until the onion starts to brown.
Add the ginger and garlic and stir for a minute.
Add the tomatoes, chili powder, turmeric and garam masala. Stir and cook until the tomato starts breaking down and the juices thicken.
Add the cooked lentils and beans. Let the dal come to a boil, then turn the heat to low and let it simmer gently for about 10 minutes until all the flavors come together.
Add the lemon juice and stir in.
Add the vegan sour cream, turn off the heat, and stir to mix the sour cream into the dal. Check seasoning and add more salt if needed.
Garnish with fresh coriander (I didn't have any, so I used some kasoori methi which I added to the dal in the final few minutes of cooking.)