Sauté the onion, carrot and celery in olive oil for 8 minutes.

Stir in the barley and bulgur and toast them together for 2 minutes so they absorb liquid more evenly.

Add the green lentils, grated tomato, thyme and vegetable stock, and bring to a boil.

Lower the heat and simmer for 55 minutes, stirring occasionally, until the grains and lentils are tender.

Season with black pepper and salt, squeeze over some lemon and serve hot; leftovers can be frozen in airtight containers once cooled to room temperature.