01 - Heat the olive oil in a large heavy-bottomed pot over medium heat. Add the diced onion, carrots, and celery. Sauté for 5 minutes, stirring occasionally, until the vegetables begin to soften and the onion turns translucent.
02 - Stir in the minced garlic, ground cumin, ground coriander, ground turmeric, and crushed red pepper flakes. Cook, stirring constantly, for about 1 minute until the spices are fragrant and toasted.
03 - Add the rinsed lentils and pour in the vegetable broth. Bring the mixture to a rolling boil, then reduce the heat to medium-low. Cover the pot and simmer for 25 to 30 minutes, or until the lentils are fully tender.
04 - Remove the pot from heat and stir in the lemon zest, fresh lemon juice, and chopped parsley. Season generously with salt and freshly ground black pepper to taste.
05 - For a creamier, smoother consistency, use an immersion blender to partially purée the soup directly in the pot, leaving some texture intact. Skip this step if you prefer a brothy, rustic soup.
06 - Ladle the hot soup into serving bowls. Garnish with additional fresh parsley and an extra squeeze of lemon juice if desired. Serve immediately.