As you can tell, you can't get this wrong. Add the quantites of most of the ingredients to your liking as you go.
Next, sprinkle a generous amount of Parmesan cheese over the sauce. Adding the Parmesan to the sauce layer helps to thicken it as it cooks.
Now repeat with another layer of ravioli, mushrooms, mozzarella, basil, spinach, sauce, and Parmesan.
For the final layer (top), place only 3 or 4 more raviolis over the layers, more sauce, then more Parmesan, and mozzarella. Add the rest of the mushrooms and sprinkle more basil, using all or some of what you have left, to your liking.
Now sprinkle Parmesan once more over everything and some freshly grated black pepper.
Turn heat to medium until the sauce starts barely bubbling through the ravioli. Turn to medium-low and simmer uncovered for 20 minutes.
Cover for cook until mozzarella topping has melted and lasagna is nice and bubbly, approximately 5 minutes.
Uncover and try not to let any moisture that accumulated on the lid drip back into the dish. Let sit for 10 minutes before serving.
Leftovers are even better, as seems to be the case with most casserole type recipes.
If you want to add meat to this recipe, brown one pound ground beef in the skillet (or half beef and half Italian sausage) until no longer pink on the outside. Drain and then remove the meat to a plate. Using the same skillet, start your layers adding the meat into the sauce layer during assembly.