Preheat oven to 425F/220C/Gas 7. Line a baking tray with baking paper.
Slice squash in half lengthwise. Remove seeds but leave skin on. Rub the squash flesh with a bit of oil. Place garlic cloves on the baking sheet and top with squash, cut side down (the squash should cover the garlic so it doesn’t burn).
Bake for 30-40 minutes, or until the skin is blistered and golden and an inserted knife comes out very easily.
While squash is cooking, bring a large pot of salted water to a boil. Cook the lasagna sheets until al dente. Drain, set aside, and gently toss with a little olive oil to prevent the sheets from sticking together.
Heat a large frying pan over medium heat. Add the olive oil and onion and sauté for 3-4 minutes or until softened, then add the mushrooms and sauté another 5-7 minutes or until lightly browned.
Then add kale, salt, pepper, and thyme (optional) and sauté for another 5-7 minutes or until tender.
Once the squash is cool enough to handle, scoop 2 cups (480g) of the flesh into a blender. Add roasted garlic cloves, cashews, lemon juice, salt, nutritional yeast and water. Blend until smooth, adding more water and scraping down the sides of the blender as needed. It should be thick and creamy.
Taste test and adjust the squash puree: more salt for overall flavour, lemon for brightness, nutritional yeast for cheesiness.
Reduce oven temperature to 350F/180C/Gas 4.
Assemble the lasagna in a glass or ceramic baking dish. Add half a cup of sauce to the bottom of the dish and spread evenly. Add a layer of lasagna sheets followed by one-third of the filling.
Repeat with two more layers of sauce, pasta and filling. Finish with a layer of pasta and the remaining squash sauce as the top layer.
Bake lasagna at 350F/180C/gas 4 for 30 minutes or until the top layer is slightly dry and a little darker in colour. Remove from oven and cool 5-10 minutes before serving.
