Heat the oil in a large saucepan. Add the diced bacon and cook for 3-4 minutes until starting to crisp.
Add the onion, carrots and celery. Cook for 5 minutes until the vegetables are softening.
Add the red lentils, potato, thyme and stock. Stir well and bring to the boil.
Reduce the heat and simmer for 20-25 minutes until the lentils have broken down and the soup is thick.
Season with salt and pepper. The bacon is already salty so taste before adding extra salt.
Serve in warm bowls with crusty bread for dipping.