In a pan on medium heat, add 2 tbsps olive oil with a third of the minced garlic. Add the chopped spinach and cook till it has wilted and darkened. Add to a bowl and set aside. Repeat with the mushrooms, cooking them till the water has evaporated and the mushrooms have lightly browned. Add to the bowl with the spinach.
Now in the same pan, add another 2 tbsps of olive oil with the remaining minced garlic, and add the diced onions. Fry till lightly golden, then add the remaining veggies. Cook till tender but not mushy. Add a very light sprinkling of salt and pepper to each component of the filling, but don't overdo it because the cheese and salt are seasoned too.
Now you're ready for assembly! Preheat the oven to 180 C.
Spread a very thin layer of the pasta sauce over the base of a 9x5 loaf tin. Soak one lasagna sheet in the hot water for about 10 seconds, then lift it out, shake off the excess water and place over the sauce in the loaf tin.
Spread about 1/3 cup of sauce over the sheet, followed by the spinach, mushrooms and veggies. Spread about 1/3 cup of cheese and 2 to 3 teaspoons of cream cheese in small dollops over the veggies.
Over this, place a second soaked noodle and repeat the process until you have three layers of filling, enclosed between the noodles.
On the topmost noodle, spread the remaining sauce and finish with the remaining cheese. Bake for about 30 minutes, until the cheese has turned lightly golden and melted, the liquid around the edges of the lasagna is bubbling away and a knife poked into the noodles goes straight through, indicating that they're cooked.
Let the lasagna rest for about 20 minutes to let the liquid get absorbed back in and for it to be easier to slice. Then use a sharp knife to cut into two large servings, or four smaller servings. Dig in immediately! Leftovers can be kept in the fridge for 2 to 3 days and in the freezer for longer, reheating in the oven or microwave as needed. Happy cooking!