Finely chop the onion, garlic, carrots, and celery. Set aside.

Heat olive oil in a large pot over medium heat. Add chopped onions, carrots, and celery. Sauté for about 5 minutes until softened.

Stir in minced garlic and sauté for an additional minute until fragrant.

Add rinsed lentils and tomato sauce to the pot. Stir well to combine.

Season with Italian seasoning, salt, and pepper. Add vegetable broth or water. Bring to a boil, then reduce heat and simmer for 20-30 minutes.

Check the consistency and adjust with more broth or water if needed.

Serve hot over pasta or with crusty bread.