Preheat your oven to 375°F (190°C). Line a baking sheet with foil or parchment paper.
In a large bowl, combine the ground chicken, Italian breadcrumbs, Parmesan cheese, egg, onion, garlic, milk, bouillon, oregano, salt, and pepper. Mix until all the ingredients are well incorporated.
Shape the mixture into a loaf and place it on the prepared baking sheet. Bake in the preheated oven for 30 minutes.
Remove from the oven and add 1/2 cup of marinara sauce over the top of the meatloaf. Continue baking for 15 minutes.
Check the temperature of the meatloaf with a meat thermometer. When it reaches 165°F, remove from the oven and top with mozzarella cheese slices. Broil for 3-5 minutes, watching carefully so it doesn’t burn. The cheese should be melted.
Allow the meatloaf to rest for 5-10 minutes before slicing to ensure it holds together well. Serve slices with the remaining warmed marinara sauce on the side.
Garnish with fresh parsley and serve with a side of garlic bread.