In a heavy bottomed soup pot, heat the oil over medium heat and sauté onion, celery, and carrots until they begin to sweat and soften, approximately 5—7 minutes.
Add the garlic, curry powder, chili powder, and sugar; cook and stir until fragrant, about 1 minute more.
Add the canned ground tomato and the vegetable stock and then bring the stock to a boil. Partially cover the pot, reduce heat to medium-low, and simmer until the vegetables are just tender, about 20 minutes.
Then, let the mixture cool slightly before removing it from heat and using an immersion blender to purée ingredients to your preferred consistency.
Return the soup to low heat; add the lentils, red peppers, cabbage, diced tomato, and navy beans. Continue cooking the soup on a low simmer until the lentils are softened, about 15 minutes. Season with salt and pepper.