Place a casserole dish on low heat with the olive oil. Put in the garlic, red and green peppers and onion, and season with a generous pinch of black pepper. Fry gently together for 10 mins, stirring regularly, or until the vegetables are just starting to soften. Add the carrot, potato, and celery and fry gently for a further 10 mins, stirring regularly.
Add the lentils and rice and stir well for about a min to coat them in the other ingredients. Pour over the stock, topping up if necessary with more liquid so the level is 4 cm above the level of the lentils and rice. Add the bay leaf and bring to boil, and then simmer for 45 mins. Taste the lentils regularly to see how they are coming along; also check the potatoes. Season to taste with salt and pepper and top up with extra water if necessary.
When the lentils and potatoes are cooked, remove the casserole dish from the heat and let it rest for 5 mins with the lid on. To serve, spoon the lentils into individual bowls and drizzle with olive oil. Enjoy with some lovely crusty bread.