Heat the 1 tablespoon of oil or 3 tablespoon of broth or water in a stock pot on medium heat. When the oil is hot, add the onion and carrots. Sauté for 5 minutes to 7 minutes, or until the onion is translucent. Stir frequently.
Add the garlic, rosemary, and rinsed lentils to the pot and stir. Cook for 2 minutes.
Add the broth and 2 cups of water and bring to a boil, then reduce the heat to simmer.
Crush the 2 teaspoon of Italian seasoning into the soup and season to your liking with salt and pepper. Stir to combine.
Cook for 25-30 minutes or until the carrots and lentils are soft, but not mushy.
Add the spinach and the lemon juice and stir. The soup is ready when the spinach has wilted.