Preheat the oven to 375°F (190°C). Lightly grease a large baking dish.
Wash the bell peppers, cut each in half lengthwise, and remove the seeds, stems, and membranes. Arrange the eight halves cut-side up in the baking dish.
Cover loosely with foil and pre-bake for 10 minutes. Remove any liquid collected inside the peppers.
Cut the chicken into bite-sized pieces and season with garlic powder, Italian seasoning, paprika, black pepper, and salt.
Heat olive oil in a large skillet over medium heat. Cook the chicken for approximately 6–8 minutes, until golden and cooked through to 165°F (74°C). Transfer to a bowl.
Reduce the heat to medium-low. Melt the butter in the skillet, add minced garlic, and cook for 30–45 seconds until fragrant.
Add the heavy cream and softened cream cheese. Whisk gently until smooth.
Gradually stir in the Parmesan, black pepper, and optional nutmeg. Simmer gently for 2–3 minutes until creamy.
Return the cooked chicken to the skillet and stir until coated. Mix in ½ cup mozzarella.
Divide the chicken Alfredo filling among the eight pre-baked pepper halves.
Sprinkle the remaining ½ cup mozzarella over the peppers. Cover loosely with foil and bake for 15 minutes.
Remove the foil and bake for another 8–12 minutes, until the peppers are tender and the cheese is melted and lightly golden.
Rest for 5 minutes, garnish with chopped parsley, and serve warm.