Using a mandolin thinly slice zucchinis to be 1/8 inch thick. Lay out onto paper towel sheets. Place more paper towel on top and gently press the water out of zucchini as best you can.
Turn oven to broil and line baking tray with parchment paper. Lay zucchini slices onto tray without crowding, and place in oven for 3 minutes. (You might have to do this in a few batches so as not to overcrowd the tray). Remove and gently flip zucchini slices to bake other side, place back in the oven for another 2 minutes. (This will help to get more moisture out of the zucchini as they contain a lot of water). Remove from oven and let cool slightly, then gently pat out any excess moisture with paper towel.
To make your vegan Bolognese: Finely chop garlic and add to a saucepan with tomato sauce, tomato paste, lemon juice and a generous pinch of salt. Bring to a simmer. Pulse lentils in blender (or food processor) and add to a saucepan. Cook sauce for 30 minutes until thick, and liquid is reduced by almost half.
Make your homemade vegan sauce. In a blender add soaked cashews (strained), nutritional yeast, garlic, lemon juice, water, onion powder (optional) and salt. Blend until creamy and smooth.
Turn oven to 375F/190C, and build your lasagna: In a 8x11 casserole, spread a thin even layer of vegan Bolognese on the bottom and layer the zucchini on top to cover. Pour a thin layer of homemade vegan cheese sauce over top of zucchini. Then sprinkle with a thin layer of vegan mozzarella cheese. Repeat the process until all your ingredients are used up (ending with the vegan mozzarella cheese, or homemade vegan cheese sauce).
Cover with foil and bake zucchini lasagna for 30 minutes. Then remove foil and bake for another 20 minutes. Let lasagna sit for 10-15 minutes before serving.