Cook the Chicken:

In a large pot or skillet (like a Dutch oven), add a drizzle of olive oil and heat over medium-high heat. Add the diced chicken and season with salt, pepper, Italian seasoning, and garlic powder. Cook for about 5 minutes, until the chicken is mostly cooked through. Remove the chicken to a plate and set aside. 
 Sauté the Onion and Garlic:

In the same pot, add the minced onion and garlic. Cook for about 2-3 minutes, until the onion is soft and translucent. 
 Prepare the Sauce:

Pour in the marinara sauce, then fill the empty sauce jar with water and add it to the pot. Stir well and bring the mixture to a boil, then reduce to a strong simmer. 
 Cook the Pasta and Chicken:

Add the chicken back to the pot along with the dried pasta. Stir to combine, then cover and cook for 10-15 minutes, stirring occasionally, until the pasta is cooked to your liking. 
 Add the Cheese:

Stir in the Parmesan cheese and 1/4 cup of the shredded mozzarella cheese. Mix well until the cheese is melted and incorporated. 
 Finish with Mozzarella:

Sprinkle the remaining 3/4 cup of mozzarella cheese on top of the dish. Cook for another 2-3 minutes, until the cheese is melted and gooey. 
 Garnish and Serve:

If desired, sprinkle with additional Italian seasoning. Garnish with fresh parsley or basil, and serve hot. Enjoy your cheesy, one-pot chicken parmesan pasta!