Bring a large pot of water to a boil. Add pasta and cook according to package instructions.
While pasta is cooking, combine ricotta, spinach, pesto, salt, pepper and parmesan in a bowl. Stir to combine and set aside.
Make bechamel sauce according to instructions. Add pesto to the sauce and stir to combine. If the sauce is too thick, add water to thin.
Drain pasta and run under cold water until cool enough to handle.
Spread 1/2 cup of creamy pesto sauce on the bottom of an 8x8 baking dish. Fill each shell with a heaping tablespoon of ricotta filling and place in the baking dish.
Pour pesto sauce over the stuffed shells.*** Place in the oven and bake for 20 minutes, or until sauce is bubbling and filling is warmed through.
Remove from the oven and serve.
Notes
*Get the recipe here.**A normal package has more than 12 shells and I would recommend cooking 15-18 in case any break while boiling. You can always eat the remaining noodles with the leftover pesto sauce. **You may have some leftover sauce.