Heat the olive oil in a large pot over medium heat. Add the onion, carrots, and celery. Cook for five minutes until the vegetables start to soften.
Stir in the garlic, thyme, and cumin. Cook for one minute until fragrant.
Add the lentils, potatoes, and vegetable broth. Bring the mixture to a boil.
Lower the heat, cover the pot, and simmer for 25 minutes. Stir once or twice during cooking.
Remove the lid and continue simmering for 10 more minutes until the lentils and potatoes are tender. Season with salt and pepper.
Ladle the stew into bowls and serve with slices of crusty bread.