Preheat oven 200°C fan forced. Heat oil in a large, non-stick frying pan over high heat. Add mushrooms, cook for 8 minutes or until mushrooms tender. Set aside to cool. Drain excess liquid.
Place the spinach onto a microwave-safe plate, cover with damp paper towel and microwave the spinach for 1—2 minutes on High/100% or until wilted. Allow to cool for 2 minutes. Squeeze to remove excess water and transfer to a large bowl. Add the mushrooms and chicken.
Combine milk or cream, ricotta, egg yolks and parmesan in a bowl. Season with salt and pepper. Grease a 5cm–deep, 16cm x 25cm (base) baking dish. Cover base with a layer of pasta. Spread with one-third of the ricotta mixture. Top with half the mushroom mixture. Repeat layers. Cover with a final layer of pasta. Spread with remaining ricotta mixture. Top with mozzarella.
Cover te lasagna with a sheet of baking paper then tightly with foil. Bake for 30 minutes, remove the paper and foil and bake a further 15 minutes or until golden. Serve with salad.