Heat oil in a large pot over medium heat. Add onion, carrots, celery, and a pinch of salt; cook 6-8 minutes until softened. Stir in garlic and cumin; cook 1 minute.

Pour in broth and rinsed lentils. Bring to a boil, then reduce heat and simmer for 15-18 minutes, until lentils are very soft and start breaking down. Stir occasionally.

Turn off heat. Using an immersion blender, blend about half the soup until creamy but still textured. Thin with water if needed.

Stir in lemon juice and most of the herbs. Taste and adjust salt and pepper. Ladle into bowls, top with remaining herbs and a drizzle of olive oil if desired.