Heat the oil in a large non-stick pan and fry the carrots, celery and garlic for 10 mins, stirring every now and then.
Meanwhile, make the vegan parmesan. Tip the cashews, nutritional yeast and garlic granules into a food processor and blitz to fine crumbs. Add a little salt, if needed, and set aside.
Tip the jackfruit into the veg mix with the lentils, 700ml water, the tomato purée, bouillon powder and thyme, then cover and cook for 25 mins. Add a little more water if needed – it should be pulpy.
Meanwhile, cook the spaghetti following pack instructions until al dente. Toss with the sauce, divide between bowls and sprinkle with the vegan parmesan and parsley, if using. The sauce will keep, covered, in the fridge for up to three days, or in the freezer for up to three months.