Using a mandoline, thinly slice the courgette lengthwise into ⅛ inch thick slices. Cover both sides with a good amount of salt and leave for 25 minutes. This is to improve taste and texture of the courgette. After 25 minutes, rinse with water to remove salt and pat dry, removing as much liquid as possible.
Turn oven to grill and line a baking tray with parchment paper. Lay courgette slices onto the baking tray without crowding, and place in oven for 3 minutes. (You might have to do this in a few batches, so you don't overcrowd the tray.) Gently flip courgette slices and bake the other side for another 2 minutes. (This will help to get more moisture out of the courgette, which is necessary to prevent the lasagne from being watery.) Remove from oven and let cool slightly, then gently pat out any excess moisture with paper towels.
To make the sauce, combine garlic, passata, tomato puree, lemon juice, and salt in a saucepan. Bring to a simmer. Pulse lentils in a blender or food processor and add to the saucepan. Cook sauce for 30 minutes, until thick and the liquid is reduced by almost half.
Preheat the oven to 190°c.
In an 8×11 inch casserole dish, spread a thin, even layer of bolognese on the bottom and layer the courgette on top to cover. Pour a thin layer of white sauce over top of the courgette. Then sprinkle with a thin layer of vegan cheese. Repeat the process until all your ingredients are used up (ending with the cheese).
Cover with foil and bake for 30 minutes. Remove foil and bake for another 20 minutes. Let lasagne sit for 10-15 minutes before serving.
