Preheat the oven to 400°F
For the béchamel sauce:
In a saucepan, melt the butter over medium low heat; you don’t want the butter to burn. Bring the heat back up to a medium high (it should be hot and golden) then add the flour. Keep stirring manually with a whisk for approximately 3 minutes. The flour should absorb the butter instantly and form a paste. Add the milk in 3 stages. Increase the heat while constantly stirring for about 5 minutes. Reduce the heat to low. Add 1/2 tsp salt and pepper. Add 1/2 cup of shredded mozzarella. Let the sauce rest until it’s time to assemble the dish.
For the Spinach:
Wash the spinach thoroughly in a big bucket of water. Drain, then remove all the excess water using a salad spinner. Roughly chop all the spinach leaves.
In a large saute pan or a big wok, heat up the oil. Add the chopped garlic, then lower the heat a bit so it does not get burnt. Stir the garlic for about 2-3 minutes until golden brown.
Add 1/3 of the amount of spinach in the pan, constantly lift the spinach leaves using 2 slotted spooned on each side of the pan. The leaves will start to wilt after 30 seconds or so. Add the other 1/3 of the spinach and repeat the same procedure for 30 seconds. Season with a little salt (this will prevent the spinach from changing color). Repeat one more time with the rest of the spinach, then transfer all the container of the pan into a big plate. Set aside the excess water from the spinach in a bowl. You can use the liquid to thin the béchamel sauce if the sauce starts to thicken too much (if desired).
In a 14” x 10” x 3” high rectangular pan lined with aluminum foil and sprayed with oil (for an easy clean up), pour the whole can of tomato sauce first, then layer 4 1/2 sheets of the lasagna. Spread a layer of spinach, salt, the sprinkle some cheese. Spread 3 ladles of the béchamel sauce, then add another 4 1/2 sheets of lasagna. Repeat until all the ingredients are used up. Finish with the rest of the béchamel sauce. It should cover the whole tray, then sprinkle the rest of the cheese.
Place in the oven for 25-30 minutes at 375°F (until golden brown).
When it’s cooked, remove the tray from the oven and let it rest for at least 20 minutes. Cut into squares, garnish with parley, freshly shaved parmesan and red chili flakes.