Warm a tablespoon of olive oil in a pan. Toss in the onion and cook for a couple of minutes on a medium to low heat. Stir in the garlic and cook until lightly golden.
Next, add the celery, carrots, red pepper, rosemary, tomato puree and chilli flakes and cook until fragrant - one to two minutes.
Pour in the chopped tomatoes and vegetable stock. Bring to the boil, then simmer until rich and lightly thickened (20-30 minutes), stirring often to prevent it from catching. Place in the blender and blitz smooth.
Add your tomato sauce back to the pan, then stir in the lentils, walnuts and mushrooms, adding in a touch of water if needed. Cook on a simmer until rich, thick and tomatoey and the lentils have softened (25-30 minutes). Stir often to prevent the bolognese from catching, adding more water if needed.
When almost ready, cook your pasta according to packet instructions. Drain, reserving some of the pasta water.
Stir 3 tbsp of pasta cooking water through your cooked bolognese. Mic in the fresh basil leaves and lemon juice, then season to taste.
Serve hot in bowls alongside cooked pasta, and top with Nutritional Yeast and a squeeze of lemon or basil leaves, if desired.