Preheat the oven to 400°F (200°C). Line a large baking sheet with parchment paper.
Slice the French bread horizontally into two long halves and arrange them cut-side up on the prepared baking sheet.
Melt 5 tablespoons of butter. Combine it with the garlic powder and chopped parsley.
Brush the garlic butter generously over the cut sides of the French bread.
Bake for 4–5 minutes, or until the surface of the bread is lightly toasted and golden around the edges. Remove from the oven.
Meanwhile, place the Alfredo sauce in a saucepan over medium-low heat. Add the remaining 3 tablespoons butter, minced garlic, onion powder, smoked paprika, salt, and black pepper.
Stir in about half of the Parmesan and cook gently until the butter melts and the sauce is smooth and warmed through. Avoid bringing the sauce to a vigorous boil.
Spread the creamy Alfredo mixture evenly over both pieces of toasted garlic bread.
Distribute the chopped chicken evenly over the sauce, then cover with shredded mozzarella and the remaining Parmesan.
Return the Chicken Alfredo Garlic Bread to the oven and bake for 8–10 minutes, or until the mozzarella is completely melted, bubbly, and lightly golden.
Let the bread cool for a few minutes before slicing. Garnish with additional fresh parsley if desired and serve warm.