Heat olive oil in a large pot over medium heat.
Add diced onion, carrots, and celery; cook until softened, about 5 minutes.
Stir in minced garlic, ground cumin, smoked paprika, and dried thyme; cook for 1 minute until fragrant.
Add rinsed lentils, diced tomatoes with their juice, and vegetable broth to the pot.
Bring mixture to a boil, then reduce heat to low and simmer, uncovered, for 30-35 minutes or until lentils are tender.
Season with salt, black pepper, and lemon juice to taste.
Serve hot, garnished with fresh parsley if desired.