Rinse lentils under cold water until clear. Chop carrots, celery, onion, and garlic into bite-sized pieces.

In a large pot, heat olive oil over medium heat. Sauté onions for about five minutes until they are translucent.

Add minced garlic, cumin, and paprika; cook for one minute until fragrant.

Stir in rinsed lentils and diced tomatoes. Mix well.

Pour in vegetable broth and bring to a gentle boil. Reduce heat to low and simmer for 30-35 minutes until lentils are tender.

Fold in spinach or kale for three minutes until wilted. Squeeze in lemon juice just before serving.