Using a mandoline slicer (if desired) or a knife, slice the zucchinis thinly lengthwise.
Lay out the strips of zucchini on paper towels and sprinkle with salt. Let them sit for 15 minutes and then wipe off the excess water.
Meanwhile, make the béchamel sauce. Warm up the milk on medium heat and stir in the salt and garlic powder.
Slowly sprinkle in the arrowroot starch while continuously stirring to reduce clumps. The sauce should thicken slightly. Remove from heat and set aside.
Preheat the oven to 400°F.
Mix together the ricotta cheese and egg.
On each slice of zucchini, layer pesto, ricotta cheese mixture, and spinach. Roll up the zucchini slice and place on its side into the baking dish or skillet.
Once you have filled the dish with zucchini roll ups, pour the béchamel sauce over the roll ups. The sauce should fill up the bottom of the dish no more than halfway.
Top the roll ups with mozzarella and parmesan cheeses and place in the oven for 30 minutes.
Once the zucchini roll ups are fully cooked and the cheese has slightly browned, remove them from the oven and let the cool slightly.
Serve the roll ups and drizzle the sauce on top. Enjoy!
Notes
(Optional) If you lightly bake the zucchini before creating the roll ups, it will roll up easier.