Lentil ragù

INGREDIENTS

• 3 tbsp olive oil
• 2 onions , finely chopped
• 3 carrots , finely chopped
• 3 celery sticks, finely chopped
• 3 garlic cloves , crushed
• 500g bag dried red lentils
• 2 x 400g cans chopped tomatoes
• 2 tbsp tomato purée
• 2 tsp each dried oregano and thyme
• 3 bay leaves
• 1l vegetable stock
• 500g spaghetti , plus Parmesan or vegetarian cheese, grated, to serve