Cut the chicken into ½-inch cubes. Season with salt and pepper.
Heat the olive oil in a large pot (we use a 4.6-quart enameled cast iron Dutch oven) over medium heat. When the oil is hot but not smoking, add the chicken in a single layer. Cook for 3–4 minutes, stirring frequently, to brown on all sides.
Take the pot off the heat. Use a slotted spoon to remove the chicken pieces and place them on a plate. Loosely tent with foil and set aside. Don’t worry if the chicken isn’t fully cooked—it will finish cooking in the soup.
Do not wash or wipe the pot. There should still be some oil left in the pan; if not, add a teaspoon or two, just enough to sauté the vegetables. Return the pot to medium heat and add the onions, carrots, and celery. Cook for 2–3 minutes, stirring often, until the onions are translucent.
Add the garlic and Italian seasoning. Stir well and cook for 1 minute, stirring frequently.
Slowly pour in the broth while stirring and gently scraping up any bits from the bottom of the pot.
Add the chicken back in. Raise the heat and bring to a boil, then lower the heat to medium-low. Cover and simmer for 10 minutes, stirring occasionally.
Add the stelline pasta to the simmering broth while stirring. Cook uncovered until tender, about 6–8 minutes, stirring occasionally to prevent sticking.
Taste and add salt if needed. As a reference, we did not add extra to ours.
Serve and garnish with chopped fresh parsley, if desired.