Heat olive oil in a large pot over medium heat.
Add diced onion, carrots, and celery, sauté until softened, about 5 minutes.
Stir in minced garlic and cook for another minute until fragrant.
Add rinsed lentils, diced potatoes, diced tomatoes with juices, and vegetable broth to the pot.
Add ground cumin, smoked paprika, dried thyme, dried rosemary, salt, and black pepper.
Bring the soup to a boil, then reduce heat to low and simmer uncovered for 35-40 minutes, or until lentils and potatoes are tender.
If using, stir in fresh spinach or kale and cook for an additional 5 minutes.
Taste and adjust seasoning if needed.
Serve hot, garnished with fresh parsley.