Cook the pasta according to the package instructions. Drain and set aside.
Heat the olive oil in a large pot. Add the celery, carrots, and onion and sauté 5 minutes until soft.
Add the chicken and cook 1-2 minutes, season with salt and pepper. Flip the chicken, add the garlic and cook an additional 1-2 minutes.
Cover with the chicken broth and bring to a boil. Boil for 10 minutes.
Remove the chicken and either cut into bite-size pieces or you can shred it using two forks.
Return the chicken to the pot, add in the cooked pasta and red pepper flakes, if using. Serve warm.