In a large bowl add the flour and the milk. Whisk very well to obtain a smooth consistency.
Add the eggs, the melted butter and adjust with a pinch of salt. Mix well.
Grease a small frying pan. I used the same one that I use to prepare pancakes. Turn the heat on at low/medium and pour one ladle of mix in the center of the pan. Gently move the pan to create a nice round shape. Let it cook for a bit more than 1 minute. Flip the cannelloni on the other side with a spatula and let it cook for another minute. You should be able to prepare 12 cannelloni. Set them apart.
Finely grate the zucchini and squeeze out the extra water with your hands.
In a large frying pan add 2 tablespoons of oil (I used grape seeds oil, but Extra Virgin Oil of Olive will be perfect too!!). Turn the heat on at medium. Add the zucchini, adjust with a pinch of salt and let it cook for 10 minutes, stirring occasionally.
In a medium size sauce pan add the butter. Turn the heat on at low and let the butter melt. Once melted add the flour and immediately whisk to create a cream.
Slowly add the hot milk and keep whisking to avoid lumps. Whisk constantly for 8/10 minutes. The flour will react with the milk creating a nice smooth sauce. You want to keep the Béchamel a bit running as we are going to bake it later. Adjust with salt and nutmeg.
ASSEMBLE THE CANNELLONI:
Add 1/2 of the Béchamel sauce in the zucchini mix (it should be more or less 1 Cup). Mix. Add the grated Parmesan cheese and the grated Pecorino cheese, mix.
Add few tablespoons of Béchamel sauce at the bottom of an oven proof container. I used one portion ceramic containers for this recipe, but you can use a big container instead.
Place two tablespoons of zucchini mix in the center of each cannelloni circle. Fold two sides of the cannelloni toward the center forming a nice cylinder. Place the cannelloni in the baking pan on top of the Béchamel. Place the remaining cannelloni one next to the other.
Sprinkle some grated Parmesan cheese on top and bake in the preheated oven at 400F/180C for 20 minutes. Enjoy!