Wash the zucchini and cut it into fine, thin slices.
Preferably on a mandoline slicer.
Clean the leek and cut it into fine thin slices.
Cut the fish into thin strips, sprinkle a bit of salt over.
Preheat the oven to 180 degrees Celsius (356 degrees Fahrenheit) (fan).
Assemble the lasagna in an ovenproof rectangular dish, approximately 22 x 30 cm.
Brush the bottom with a thin layer of olive oil, cover with lasagna sheets.
Spread a thin layer of spinach sauce over the sheets, add a layer of fish, zucchini, and leeks, followed by good spoonfuls of tomato sauce.
And again a layer of lasagna sheets, spinach sauce, fish, zucchini, leek, and tomato sauce.
And so on.
Finish with lasagna sheets and on top of them, the last of the spinach sauce.
Sprinkle with a bit of extra Parmesan.
Bake for about half an hour until the lasagna is golden and delicious.
Keep a close eye on it, it may be necessary to cover with foil along the way so the lasagna doesn't burn.
Place a stack of plates and the lasagna on the table – call friends and family and dig into the delicious and steaming hot fish lasagna.
Serve with a simple green salad.