Preheat oven to 180°C/160°C fan-forced and spray a baking dish with oil.
Heat a large non-stick frypan over medium-high heat. Spray with oil and cook onion, stirring for 5 mins until soft.
Add garlic and cook for another minute.
Add mushrooms, chilli flakes and season with salt and pepper. Continue to cook, stirring occasionally, for 5-8 mins or until browned.
Stir through tomato paste, tomatoes, water and basil. Bring to a low simmer and cook for 15 mins or until thickened. Remove from heat.
Combine ricotta and spinach in a medium bowl and season with salt and pepper.
To assemble, ladle ½ cup of sauce to cover the base of the baking dish and top with 1 ½ sheets of lasagna or enough to cover the whole base.
Spread one third of the sauce over the pasta then dollop and spread one third of the ricotta on top.
Add another layer of pasta, half the remaining sauce, then half the remaining ricotta.
Add the remaining pasta, sauce and ricotta and scatter over mozzarella.
Spray a piece of foil with oil, cover and bake for 30 minutes.
Remove the foil, return to the oven and cook for another 3-4 minutes or until cheese is golden.
Garnish with fresh basil.
