Preheat the oven to 180 degrees celcius.
Combine mushrooms, 400g diced tomatoes, garlic and oregano in a small bowl.
In another bowl, combine ricotta, spinach, half the mozzarella, salt and milk.
In a large lasagne dish pour 400g of diced tomatoes into the base of the dish, spreading it out evenly.
Build your layers: Layer 1: Add a layer of the pasta sheets (2), pressing down gently. Layer 2: Add 1/3 of the tomato/mushroom mix, spread evenly to edge. Layer 3: Add 1/3 of the ricotta/spinach mix, spread evenly to edge. Layer 4: Sprinkle with 1/4 of the remaining mozzarella. Repeat layers 1-4 until you have finished (Ideally ending with mozzarella).
Sprinkle evenly with parmesan and place in the oven. Cook for 25 minutes covered with aluminium foil. Remove foil and cook for a further 25 minutes till golden brown. Enjoy!