Cook the frozen breaded chicken on a sheet pan according to its package directions. Let it cool for approximately 5 minutes, until comfortable to handle.
Preheat a conventional oven to 350°F (177°C). Lightly coat a 12×8-inch baking dish with nonstick cooking spray.
Combine the melted butter, garlic, onion powder, Italian seasoning, and crushed red pepper flakes in a small bowl.
Slice the rolls horizontally. Place the bottom halves in the prepared dish and brush them with some garlic butter.
Cover the roll bottoms with 6 mozzarella slices. Spread ½ cup marinara over the cheese, then arrange the cooked chicken evenly over the sauce.
Drizzle the remaining ½ cup marinara over the chicken. Sprinkle with 1 Tbsp Parmesan and cover with the remaining 6 mozzarella slices.
Add the roll tops. Brush with the remaining garlic butter and sprinkle with the remaining 1 Tbsp Parmesan.
Loosely cover with foil and bake for 20 minutes. Uncover and bake for another 3–5 minutes, until the mozzarella is fully melted, the edges bubble gently, and the tops are lightly golden.
Garnish with parsley, if using. Cut along the roll divisions and serve warm with optional additional marinara.