If you haven't already, put the cashews for the cheese sauce to soak - cover them with plenty of boiling water and set aside for half an hour. Alternatively you can soak them in cold water overnight.
For the tomato sauce, heat the sundried tomato/olive oil in a large pan over a low heat. Add the chopped onion, celery and carrot and cook gently for about 10 minutes until softened. Stir often.
Add the sliced chestnut mushrooms, crushed garlic and chopped sundried tomatoes and continue to cook until the mushrooms are soft and most of the excess water has evaporated.
Add the tomato puree and red wine and cook until most of it has evaporated then add the tinned tomatoes, oregano, thyme, sugar, chilli flakes if using, vegetable stock cube, water and frozen spinach. Simmer for about 15-20 minutes then season to taste with salt and pepper.
While the sauce is simmering, cook the sausages according to the packet instructions. Once they and the tomato sauce are both cooked, thinly slice the sausages and stir them through the sauce.
Meanwhile, cook the pasta in salted boiling water for two minutes less than the packet instructions then drain well.
To make the ‘cheese’ sauce, drain the soaked cashews and put them in a blender with the water, clove of garlic, nutritional yeast, olive oil or refined coconut oil, cider vinegar, salt and tapioca starch or cornflour and blend until completely smooth.
Preheat the oven to 180°C/350°F/gas mark 4.
Toss the cooked pasta through the tomato sauce then tip half of it into a lasagne dish (mine is 32 x 25 x 7cm / 12 ½ x 10 x 2 ¾ inches) and spread level. Drizzle about a third of the white sauce over the top.
Top with the rest of the pasta then pour the rest of the white sauce over the top. Bake for about 30 minutes until golden and bubbling.