This makes at least 6 portions. You could leave out the aubergines and courgettes and put in more peppers, maybe add finely chopped carrot and celery/fennel.
Chop smallish and roast two aubergines, three courgettes, two or three red onions, two or three red/yellow/orange peppers, lots of garlic, box of mushrooms, with olive oil, salt, black pepper, oregano, basil. Mix in a tin of chopped tomatoes, some chopped black stoned olives, capers, sundried tomato paste.
Cook best part of a packet of frozen spinach and drain thoroughly. Mix with two little tubs of ricotta, grated nutmeg, salt and pepper.
Layer up lasagne sheets and tomato veg mixture. About three layers of lasagne should do it. Ricotta mixture goes over top layer of lasagne sheets. Put lots of grated Parmesan across top. Bake for at least 40 minutes.
Mozzarella could be incorporated in some way.
Another option would be to make something more like a traditional meat lasagne by using a lentil bolognese sauce instead of a meat ragu.