Add the marinara sauce to a wide skillet over medium heat. Bring to a simmer.
Add the chicken, cutting into bite-size pieces with a pair of kitchen scissors as you drop into the sauce.
Cover, reduce the heat to low-medium so the sauce is at a low simmer, and cook for 5 minutes.
Remove cover, flip the chicken over, and cook for an additional 5-8 minutes, or until the chicken is fully cooked. (It should register 160 degrees F on an instant-read thermometer.)
Meanwhile, prepare the pasta if using. Drain.
Stir the butter and Parmesan cheese into the chicken mixture. Season to taste with salt.
Serve the chicken in tomato sauce over the pasta. Top with additional Parmesan cheese, if desired.