Heat oil in a pan. Add chopped onion and cook for 2–3 minutes until soft. Add garlic and stir for 30 seconds. Add ground chicken and cook it until no longer pink. Add salt, pepper, and Italian seasoning.
Pour in the marinara sauce. Stir everything together. Let it cook on low heat for 5–7 minutes so the sauce thickens.
Turn off the heat. Add half the mozzarella cheese and all of the Parmesan. Stir it until everything melts and looks creamy.
If you want, mix some butter and garlic powder. Spread on the inside of each bun. Toast in a pan or oven until golden brown.
Put the chicken mixture on each bun. Sprinkle with the rest of the mozzarella. You can broil it in the oven for 1–2 minutes if you want the cheese melted on top. Add basil or parsley if you like.