Preheat oven to 375F.
Spray a 13x9 baking dish with cooking oil spray.
Spread about ½ cup of the pesto béchamel sauce at the bottom of the casserole.
Place three lasagna sheets on top of the sauce. Break about ¾ of a fourth one to cover the whole bottom. Put in any broken pieces too do not throw them away they will all cook and mend together no-one will notice the broken pieces.
Add ½ of the cheese mixture, about 1 cup, spreading it over the noodles. Top with ½ of the pesto béchamel sauce about 2 cups.
Sprinkle 1 cup of the shredded mozzarella on top.
Repeat the layers of lasagna, the remaining cheese mixture followed by the remaining pesto béchamel then 1 cup of the mozzarella cheese.
For the final layer, add noodles then top with the béchamel sauce we already set aside then sprinkle the remaining cup of cheese on top.
Cover and bake for 50 minutes.
Remove cover and bake uncovered until top is golden brown, 10-15 minutes. You can also turn on the broiler to get a nice dark top but watch for it as it might burn easily.
Let it rest for at least 20 minutes before cutting and serving.