Preheat your oven to 400°F (200°C).

In a large mixing bowl, combine shredded cooked chicken with marinara sauce, garlic powder, salt, and pepper. Mix well.

Carefully slice your sub rolls or baguettes lengthwise, keeping one side intact.

Brush the inside of each sliced roll with olive oil.

Carefully fill each roll with the chicken mixture, pressing down slightly.

Sprinkle shredded mozzarella cheese over the filled sandwiches. Add grated Parmesan if using.

Place sandwiches on a lined baking sheet and bake for 10-12 minutes until golden brown.

Remove from the oven, allow to cool slightly, and garnish with fresh herbs before serving.