Preheat oven to 375 F (190 C)
Get your lasagna pan out, it doesn't really matter the size, use any sort of rectangle or square dish you have.
Slice off the top part of the garlic bulb (not a lot, but enough so that when it's roasted, you can squeeze out the garlic). Place it either in a dish or in tinfoil and drizzle with a bit of oil, pinch of salt and pepper. Close up the tinfoil or cover the dish and place in the oven for 15-20 minutes until roasted and so fragrant.
While the garlic is roasting, thinly slice the zucchini. You can absolutely make your own tomato sauce, I personally prefer to use a jar.
When the garlic is done, carefully squeeze it out into a blender or food processor. It will be HOT so use an oven mitt.
Add in the rest of the bechamel ingredients and blitz until creamy. Add in a few Tbsp of water at a time to thin out.
Place a few Tbsp of tomato sauce on the bottom of the lasagna pan and spread around with the back of a spoon.
Place the zucchini "noodles" on top of the sauce. Add a few more Tbsp of tomato sauce and spread out. Then, pour some bechamel sauce on top and spread around. Toss some spinach on top. Then layer with the zucchini "noodles" and do it all over it again.
Make sure you finish the lasagna (i.e. the top layer) with bechamel sauce. If you like, sprinkle a bit of almond flour (to resemble parmesan) or real parmesan on top.
Cover the pan with a lid or tinfoil, then place in the oven and cook for 35 minutes, uncover and bake for another 15 minutes. If you want the top to be a bit crisp, broil for 3-ish minutes but watch it so it doesn't burn
When slightly cooled, slice into pieces and enjoy.