• Put the mushrooms and frozen spinach/kale in a microwave safe bowl. Mix in the olive oil and a pinch of salt. Microwave for 4 minutes, stirring once, until the mushrooms are soft and liquid has released from the mushrooms and spinach. 
• Transfer the mushrooms and spinach into a colander over the sink to drain out any liquid that has collected in the bowl. Shake the colander a few times and press against the mushrooms and spinach with a spoon to release more liquid. Get out as much liquid as you  can, but don’t spend too much time on this. Some liquid remaining with the mushrooms and spinach is perfectly fine. 
• 
• In a separate bowl, mix together the ricotta cheese and creme fraiche. If you want, you can also mix in chopped fresh basil.
• In a third bowl, combine the mozzarella and parmesan. 
• Take your three bowls (mushroom&spinach, ricotta&creme fraiche, mozzarella&parmesan) and set them next to the slow cooker with the marinara sauce and uncooked noodles. 
• Brush a thin layer of olive oil over the bottom and sides of the crockpot insert (or spray with cooking spray).
• Spread ½ cup of marinara sauce over the bottom of the crockpot. 
• Layer the ingredients in the crockpot in this order (in total, you will make 3 complete layers):
  - 3 to 4 lasagna noodles (you will need to break up some of the noodles to fit in the crockpot. This is fine, all the pieces will meld together as they cook)
  - 1 cup of the ricotta/creme fraiche mixture (spread evenly with a spoon)
  - ½ cup of mushrooms and spinach (spread out with a spoon)
  - 1 cup marinara sauce (spread evenly with a spoon)
  - 1 cup grated mozzarella/parmesan
• After making 3 layers, finish with a layer of noodles, ½ cup red sauce and 1 cup grated mozzarella/parmesan cheese. 
• Cover and cook for about 3 hours on low heat (see cooking note below). You'll know the lasagna is cooked when the noodles are tender, the cheese is melted, and the edges are slightly browned but not burnt.
• Turn off the heat and let lasagna sit for 30 minutes before slicing and serving. 

Cooking Notes: The "low" and "high" settings on slow cookers tend to vary in how much heat they put out, which is why most slow cooker recipes give an approximate, not an exact, cooking time. My Hamilton Beach crockpot is 10 years old and the "low" setting gets quite hot -   I rarely use the "high" setting. In my crockpot, 3 hours on low is plenty of time to cook the noodles. However, all slow cookers are different. If your crockpot doesn't get as hot and the noodles aren’t tender after 3 hours, you'll need to extend the cooking time to 4 hours.