Bring 2 cups of salted water to a boil in a medium saucepan. Add the dry pasta and cook for about 10 minutes, or until tender.
While the pasta cooks, slice the chicken and chop the onion and bell pepper.
Heat olive oil in a large heavy-duty pan or pot over medium-high heat.
Add the onion and bell pepper. Sauté for 1 to 2 minutes until slightly softened.
Add the minced garlic and cook for 30 seconds, until fragrant and lightly golden.
Add the chicken, salt, pepper, and garlic powder. Cook until the chicken is browned and nearly cooked through.
Pour in the marinara sauce, cover the pan, and let it simmer for 5 minutes.
Drain the pasta and add it to the chicken mixture. Stir well so the sauce coats everything evenly.
Add the mozzarella or Italian blend cheese and turn off the heat. The cheese will melt into the Quick and Easy 15 Minute Chicken Pasta from the warmth of the pan.
Sprinkle with Parmesan, if using, and serve warm. For a bubbly top, broil briefly in the oven before serving.