Start by chopping the onion, carrot, celery, and garlic into small even pieces. Uniform cuts help the vegetables cook evenly and blend smoothly into the soup. Fresh vegetables always give the soup a brighter and more homemade flavor.
Heat olive oil in a large pot over medium heat and add the onion, carrot, and celery. Cook for about 5 to 7 minutes until the vegetables soften and the onions become translucent. Stir in the garlic, cumin, turmeric, black pepper, and salt for another minute until fragrant.
Rinse the red lentils under cool water to remove excess starch before adding them to the pot. Pour in the vegetable broth and stir everything together thoroughly. Bring the soup to a gentle boil so the lentils can begin softening properly.
Reduce the heat to low and let the soup simmer uncovered for about 25 minutes. The lentils will break down naturally and create a creamy texture without needing dairy. Stir occasionally to prevent the lentils from sticking to the bottom of the pot.
Once the soup becomes thick and creamy, stir in the fresh lemon juice. The lemon brightens the entire soup and balances the earthy cumin perfectly. Taste the soup and adjust the seasoning if needed before serving.
Ladle the hot soup into serving bowls and sprinkle fresh parsley on top. Add a lemon slice for extra freshness and visual appeal. Serve immediately while warm for the best comforting flavor.