In a skillet, heat 1 tbsp of the olive oil on medium high heat.  Add the onions and soften. Next add the tomatoes and garlic and cook until the tomatoes begin to blister. With an immersion blender, puree the vegetables.  Add the san marzano tomatoes and cook down for 10 minutes.  Break up with a wooden spoon while cooking and continue to simmer for 20 minutes.

Remove from the pan and add the second tbsp of olive oil.  Add the spinach and cook until it wilts - season with salt and pepper as you cook.  Once cooked let cool.  Once cool, squeeze out the remaining water.

Layout the sliced eggplant and drizzle the Kosher salt on the slices pulling out the moisture. 

In a 13" x 9" glass baking dish, begin layering the lasagna.  Begin by putting the marinara sauce on the bottom.  At this point, you can really layer in any order you want.  I did 3 layers of eggplant and 2 layers of zucchini.  Mix sauce between most layers and add cheese in most layers.  Finish with an eggplant layer and top with cheese.  I also should make clear that I seasoned each layer with spice as I layered the dish.

Add to a 450 degree oven and bake for 30 minutes.

Serve and enjoy!