Prepare the vegetables by chopping the onion, carrots, celery, and mincing the garlic.
In a large pot, heat olive oil over medium heat. Sauté the onion, carrots, and celery for 5–7 minutes until softened. Add garlic and spices; sauté for an additional minute.
Stir in rinsed lentils, vegetable broth, and diced tomatoes; bring to a boil then reduce heat. Cover and simmer for 25–30 minutes until lentils are tender.
Add kale or spinach; cook for another 5 minutes until wilted. Stir in lemon juice and season with salt and pepper to taste.
Serve hot with optional toppings like fresh parsley or yogurt.