Start by heating the olive oil in a large pot over medium heat. Once warm, add the chopped onion, diced carrots, and celery. Stir regularly as they soften and release their aroma—this process typically takes about 5 to 7 minutes. Add in the minced garlic toward the end and cook for another minute, being careful not to let it brown.
Once the vegetables are softened, it’s time to build the flavor. Stir in the cumin, paprika, turmeric (if you're using it), and a pinch of salt. Let these cook for about a minute to bloom the spices. This short step deepens their taste and infuses the base with warmth and color.
Pour in the rinsed lentils along with the vegetable broth, diced tomatoes, and bay leaf. Stir everything together to combine, then bring the mixture to a boil. Once it reaches a steady bubble, reduce the heat to low, cover the pot, and let it simmer gently for 30 to 40 minutes. Stir occasionally to make sure nothing sticks to the bottom.
After the lentils are soft and the soup has thickened, remove the bay leaf. Taste the soup and adjust the seasoning with additional salt and freshly ground black pepper if needed. For added brightness, squeeze in fresh lemon juice and stir through just before serving.
Ladle the hot soup into bowls and garnish with chopped fresh parsley for a burst of color and herbaceous freshness. Serve immediately with warm, crusty bread or a light salad to round out the meal. Leftovers store well and taste even better the next day.