Heat a medium-large pot on medium heat with olive oil. Fry onion, garlic and thyme. Add potatoes, carrots and tomatoes. Stir and cook for 2 minutes.
Pour vegetable broth and green beans. Stir and cook for another 2 minutes. Add lentils and stir well. Bring to simmer then turn to low medium heat, cover and cook for about 20 minutes until carrots and potatoes are tender.
Adjust taste with salt and pepper. Remove from heat.