Preheat oven to 400°F. In a large skillet, heat the olive oil over medium heat. Once hot, add the chicken and cook until browned, about 5 minutes. Remove from the skillet with a slotted spoon and set aside.
1 tablespoon olive oil, 1 pound boneless, skinless chicken breasts
In a large pan bring 4 cups of water to a boil then add jumbo shells. Cook to al dente, about 10 minutes. Remove from heat and strain.
12 ounces dry jumbo pasta shells
In a medium bowl, mix the cooked chicken, ricotta cheese, three-quarters of the Parmesan cheese, and Italian seasoning together. Cover the bottom of a 9x13-inch baking pan with a thin layer of marinara sauce.
15 ounces ricotta cheese, 5 ounces Parmesan cheese, 1 tablespoon italian seasoning
Fill each shell with the chicken mixture and place it in the baking dish. Once all shells are filled pour the remaining sauce evenly over the shells then sprinkle the remaining Parmesan cheese over top.
24 ounces marinara sauce
Bake in the preheated oven for 20 minutes. Remove from the oven and serve.