Add the oil to a large soup pot and bring the heat to medium.
Add the cumin seeds and mustard seeds and stir for 1 minute.
Now, add the onion, garlic, and ginger and cook for about 5 minutes.
Add the coriander, ground cumin, turmeric, garam masala, and chili powder. Stir for 1 minute to coat the aromatics.
Now, add the carrot and red pepper and cook for about 5 minutes.
Add the cabbage and potatoes and stir for 1 minute.
Add the lentils, tomatoes, broth, salt, and black pepper.
Bring to a boil, cover, then simmer for 40-45 minutes, or until the lentils are tender.
Add the lemon juice, optionally top with chopped parsley, and serve.
