Heat olive oil in a large pot over medium heat and sauté the onion and garlic until fragrant.
Add the diced carrots and cook for 3–4 minutes.
Stir in the lentils, vegetable broth, and cumin, then bring to a boil.
Reduce the heat and simmer for 25–30 minutes, or until the lentils are tender.
Add the fresh spinach and cook for another 2–3 minutes until wilted.
Season with salt and black pepper to taste.
Serve hot with a squeeze of fresh lemon juice or whole-grain bread if desired.