Step 1: Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion, carrots, and celery. Sauté for 8-10 minutes, stirring occasionally, until the vegetables have softened and the onion is translucent.
Step 2: Stir in the minced garlic, ground cumin, ground coriander, turmeric, and dried thyme. Cook for another 1-2 minutes, stirring constantly, until the spices are fragrant.
Step 3: Add the rinsed lentils, diced tomatoes (undrained), and vegetable broth to the pot. Stir well to combine. Add the bay leaf.
Step 4: Bring the soup to a boil, then reduce the heat to low, cover, and simmer for 25-35 minutes, or until the lentils are tender. The cooking time can vary slightly depending on the age of your lentils. Check for tenderness around the 25-minute mark.
Step 5: Remove the bay leaf. Use an immersion blender to partially blend the soup if you prefer a thicker, slightly creamier consistency. Alternatively, scoop out about 1-2 cups of the soup, blend it in a regular blender (carefully!), and return it to the pot. This step is optional but highly recommended for a richer mouthfeel.
Step 6: Stir in the fresh lemon juice and chopped fresh parsley. Season with salt and black pepper to taste.