PREP: Preheat the oven to 350 degrees F. Lightly spray a 9x13-inch baking dish with cooking spray and set aside.
PASTASHELLS: Bring a large pot of water to a boil. Add a generous amount of salt (1 teaspoon for every 4 cups) and then add in the pasta shells. I usually cook a few extra in case some fall apart. Cook for 1 minute less than the package says to al dente. Drain the shells and rinse under cold water to stop the cooking and allow them to be easily separated. Drain off any water and separate shells onto a sheet of parchment paper on the counter.
CHEESEFILLING: Place the ricotta cheese, 1 cup mozzarella cheese, egg, Parmesan cheese, 1/4 cup chopped basil, dried oregano, dried thyme, dried parsley, and minced garlic in a large bowl. Season with salt and pepper (I add 1 teaspoon salt and 1/2 teaspoon pepper). Stir until combined. Transfer this cheese mixture to a large (gallon sized) zippertop plastic bag. With scissors, snip 1-inch off the corner of the bag and "pipe" the cheese mixture into each of the 32 shells. Each shell should get a heaping 1 tablespoon of the cheese mixture (which should fill 32 shells just over halfway full).
ASSEMBLY: Spread 1 cup of the marinara sauce along the bottom of the prepared baking dish. Add cheese-stuffed shells in baking dish on top of the marinara. Press the chopped chicken pieces into each shell on top of the cheese mixture, using up all the chicken. Spoon remaining sauce over stuffed shells, being mindful to cover all the pasta so it doesn't dry out during baking.
BAKE: Cover dish with foil; bake 30 minutes. Remove the foil and sprinkle the top with the remaining 1 cup mozzarella cheese. Bake uncovered 10-15 minutes longer or until cheese is melted.
TOPPING: Meanwhile, in a nonstick skillet, heat oil over medium heat. Add panko; stir to coat. Cook and stir 2 to 4 minutes or until golden brown. Sprinkle over baked shells along with remaining 2 tablespoons basil. Enjoy hot!
Note 1: I use Tyson's ® crispy chicken strips and bake according to package directions. Once baked, I let slightly cool and then chop into small bite-sized pieces.