Preheat oven to 220°C/200°C fan-forced. Lightly grease a 2.5 litre (10 cup) oven proof dish.

Slice 100g of the mushrooms and set aside for the top. Chop remaining mushrooms into 1cm pieces. Heat oil in a large, non-stick frying pan over medium heat. Add onion and garlic. Cook, stirring for 2 minutes or until onion softens.

Add chopped mushrooms. Cook, stirring for 7 minutes or until beginning to golden. Stir in lentils, passata and 1 cup water. Bring to a gentle boil. Simmer, partially covered on low for 15 minutes until thickened. Season with salt and pepper and remove from heat.

Whisk together the ricotta, egg, and milk. Season with salt and pepper. Stir through 1 cup of Perfect Bakes cheese. Refrigerate until ready to use. Reserve remaining cheese.

Spread 1/3 of the mushroom mixture over base of dish. Top with lasagne sheets, trimming to fit the size of the dish if necessary.

Top lasagne sheet layer with another third of the mushroom sauce and sprinkle with 3/4 cup of Perfect Bakes cheese then cover with another layer of lasagne sheets. Continue with remaining third mushroom sauce, another 3/4 cup of cheese, and remaining lasagne sheets.

Squeeze liquid from thawed spinach. Sprinkle spinach over the last lasagne sheet then spread ricotta mixture over the top. Sprinkle with 1 cup Perfect Bakes cheese and arrange reserved mushroom slices on top. Spray with oil.

Cover with a sheet of greased baking paper and foil and bake for 35 minutes. Uncover. Bake uncovered for 15-20 minutes until golden and lasagne sheets are cooked. Stand 10 minutes before serving. Serve with fresh green salad.