Heat olive oil in a large pot over medium heat.
Add diced onion, carrots, and celery. Sauté for 5 minutes until softened.
Stir in garlic and cook for 1 minute until fragrant.
Add lentils, diced tomatoes, broth, cumin, paprika, turmeric, salt, and pepper. Stir well.
Bring to a boil, then reduce heat and simmer for 30–35 minutes until lentils are tender.
Stir in spinach (or kale) and cook for 5 more minutes.
Remove from heat and add fresh lemon juice.
Ladle into bowls, garnish with parsley, and serve warm.