Veggies: Add a drizzle of oil to a large pot over medium heat and add mushrooms, courgette/zucchini, aubergine/eggplant and red pepper. Fry until soft right through and starting to char, then remove to a side bowl. Add a drizzle more oil then add carrot, celery, onion and garlic. Continue frying until they soften/begin to brown then add back in your fried veggies and mix everything together.
Veggie Sauce: Pour in tomato passata, swill out the jar/cartons with 1 cup/250ml water and pour that in too. Add basil and oregano, then add sugar, salt, chilli flakes and pepper (all to taste). Allow the sauce to simmer on low for around 20-25mins, or until it turns nice and thick. If it's too watery just continue simmering for another 5 or so mins (see video for ideal texture).
Spinach Ricotta: Meanwhile in a large mixing bowl add ricotta, mascarpone, egg, parmesan, salt, pepper and nutmeg. Combine with a hand mixer until smooth, then fold in thawed spinach with a spatula until evenly incorporated.
Lasagne: In an 8x12" baking dish (or similar size) add a couple of spoonfuls of veggie sauce to the base of the dish. This is so the pasta doesn't stick to the bottom. From there your layers will go as follows: Pasta Sheets, Veggie Sauce, Spinach Ricotta, Mozzarella. The last layer will be Pasta sheets, then Spinach Ricotta, then Mozzarella and Parmesan to top. That's 4 layers of pasta, 4 layers of Veggie Sauce (including very bottom layer), 4 layers of Spinach Ricotta and 4 layers of Mozzarella.
Bake & Serve: Pop in the oven at 350F/180C for 30-40mins or until crispy and deep golden on top. Allow to rest for 10mins before serving (this is important or it will be too liquidy). Serve up and enjoy!