Bring a large pot of heavily salted water to a boil and boil pasta shells al dente according to package directions. Drain.
In a large skillet, heat the olive oil over medium-high heat and add the chicken. Season with salt and the Italian seasonings. Cook chicken 5-6 minutes or untll chicken is no longer pink. Let mixture cool.
Preheat oven to 350 degrees F.
In a medium bowl, combine the cooled chicken, ricotta, 1 cup of the Mozzarella cheese, Parmesan cheese, egg, garlic, and salt.
Pour 2 cups of the marinara sauce on the bottom of a 9x13 inch pan.
Spoon about 2 tablespoons of filling into each pasta shell and place filling side up.
Pour the remaining marinara sauce on top of the shells and sprinkle with remaining 1 cup of mozzarella cheese. Sprinkle Panko breadcrumbs on top of the cheese.
Cover with nonstick foil or spray the bottom side of the foil with cooking spray and cover. Bake for 20 minutes. Remove the foil and bake for 5-10 minutes or until Panko crumbs are brown.