Heat oven to 375°F. Spread 2 cups marinara in a 9x13-inch baking dish.
Boil shells in salted water until barely al dente, 1–2 minutes shy. Drain and rinse.
Toss shells with 1 teaspoon olive oil so they don’t stick. Set aside to cool slightly.
Combine chicken, ricotta, 1½ cups mozzarella, ½ cup Parmesan, egg, parsley, garlic, seasoning, salt, and pepper.
Stir in red pepper flakes if using. Mix until evenly combined and scoopable.
Make topping: mix panko, remaining ¼ cup Parmesan, and 1 tablespoon olive oil with a pinch of salt.
Toast topping in a skillet over medium heat 2–3 minutes, stirring, until lightly golden. Cool briefly.
Fill each shell with 2–3 tablespoons of the chicken mixture.
Nestle stuffed shells over the sauce. Spoon remaining 1 cup marinara across the tops.
Sprinkle remaining ½ cup mozzarella over shells, then scatter the toasted breadcrumb topping.
Cover with foil and bake 20 minutes. Uncover and bake 10–15 minutes, until bubbling and browned.
Rest 5 minutes before serving. Garnish with extra parsley and serve hot.
Notes
Variation: Swap panko with crushed garlic croutons for extra crunch, or drizzle with a little pesto before serving. Make-ahead: Assemble up to one day in advance, cover, and refrigerate. Add 5–10 minutes to the covered bake time.This recipe is an original creation inspired by classic Easy Chicken Parm Stuffed Shells flavors. All ingredient ratios and instructions are independently developed.