Start by cooking the green lentils in a pot of boiling water according to the package instructions. Add the stock cube to the boiling water and dissolve before adding the lentils.
If you are using whole walnuts, blitz the walnuts in a food processor or bash them with a pestle and mortar until they are ground up.
Add a tablespoon of oil to a pot, then add the chopped onions and cook for a few minutes until the onions start to soften. Add the chopped garlic to the pan and cook for another minute or two.
Add the chopped carrots and celery along with the herbs. Cook for anther 2 minutes, stirring everything regularly.
Add the chopped tomatoes to the pan and the tomato puree along with 100 ml of water
Add the red wine vinegar, balsamic vinegar and ground walnuts.
Drain the lentils once they are cooked, but reserve the water to add to the bolognese sauce if needed.
Add the lentils to the pot and mix in the bolognese sauce.
Add the salt and pepper to taste and bring it to simmer and cook for 15 minutes
While simmering, cook the pasta in boiling water following the instructions.
When cooked, drain the spaghetti in a colander.
Serve the bolognese sauce with the cooked spaghetti, along with a sprinkle of parsley to garnish.