Heat olive oil in a large pot over medium heat. Add the onion, carrots, and celery and cook until vegetables are softened, about 5 minutes.
Add the garlic, cumin, paprika, turmeric, and dried thyme. Cook for another minute until fragrant.
Add the black lentils, vegetable broth, and diced tomatoes to the pot. Bring to a boil, then reduce heat to low and simmer for 30 minutes.
Add the chopped vegetables and simmer for an additional 10-15 minutes, until all the vegetables are tender.
Season with salt and pepper to taste. Serve hot, garnished with fresh cilantro.