Preheat oven to 375F°. Begin cooking your ground beef in a large skillet. Drain of grease if too much pools up. Cook until no longer pink and some pieces have begun browning. Transfer to a bowl and set aside.
In a large frying pan, heat up 1 tbsp of olive oil over medium heat. When your oil has warmed up, toss in garlic and mushrooms. Cook for 5 minutes or until mushrooms are tender. Add spinach a handful at a time. Cook for 1 to 2 minutes or until spinach is wilted. It won't be wilted in a brown and dead kind of way. It will have a very wet and sloppy appearance. Transfer your spinach and mushroom mixture to a medium bowl. Stir in basil. Set aside.
In a small bowl, combine egg, salt, pepper, parmesan and ricotta cheese. Mix well.
Cook lasagna noodles according to package directions. I almost always cook my pasta for 11 minutes unless a recipes says to do something different. The original recipes call for cooking the lasagna first but that annoyed me in the end because it allowed the noodles too much drying time. When your noodles are ready, drain and allow to cool. Then using a large plate, lay 3 or 4 strips in one direction. Add a layer ontop going the opposite direction and continue with this pattern.
Coat a cookie sheet with foil. Prepare a springform pan with a spritz of your favorite oil and place on your cookie sheet. Lightly coat the bottom of your pan with sauce. Roughly 1/2 cup should do the trick. You don't want it too sloppy, it's just to keep your noodles from baking directly to the pan. Using a total of less than 3 complete pieces, make a layer of lasagna noodles in your pan. Trim the edges. I always started with the furthest spot away from me and moved towards me with the noodles. Reserve trimmed pieces to fill in smaller gaps. I found there was always an inch or so closest to me that needed noodles. A full piece of lasagna would have been a waste so the trimmings came in handy.
Top of noodles with half of your spinach and mushroom mixture. Then coat with half of your cheese mixture, spreading out nice and evenly. Using a large spoon or baking spatula to push or press down on the cheese helps to make it smoosh down without needing to really attempt to spread it. If you try to spread it in any other way your spinach and mushrooms will penetrate the cheese. This isn't a big deal but I just found it to be annoying to try to spread, so that gives you an easier way to smoosh it in there. Plop a spoonful and smoosh, repeat. Easy enough.
Make another layer with noodles, trimming and reserving the extra pieces as necessary. Pour in a third to half of your remaining sauce. Top with ground beef and sprinkle with cheese.
Repeat layers, finishing up your spinach and mushroom mixture as well as your cheese mixture. You may or may not use all of your ground beef. If you don't use all of it, use for another meal or freeze for a later use. To finish, make one more layer of noodles. Spread around a small amount of sauce and sprinkle with any remaining cheese.
Bake for 45 minutes on your prepared cookie sheet. This will catch any possible leaking sauce.
Let sit for 5 minutes. Transfer entire lasagna to a large platter. Run a knife between lasagna and the edge of your pan. Carefully release and remove springform pan side. Slice and serve.