Preheat oven to 375 F.
Slice eggplant or zucchini (or a mixture of both) thinly, longways, with a mandolin if you have one, or use a knife carefully, making long planks.
Roast on a sheet pan until wilted and lightly brown, about 10 minutes.
Sauté onions and beef over medium-high heat, add in mushrooms if using and brown. Add sauce and if using spinach add now.
Layer as follows:- sauce- uncooked lasagna noodles (or veggie noodles)- yogurt- sauce- sliced mozzarella
Bake for about 40-50 minutes until bubbly and cheese is melted.