Cut the chicken breasts into roughly 1-inch pieces so they cook evenly.
Heat 1–2 tablespoons olive oil in a Dutch oven or large heavy skillet over medium heat.
Add the chicken pieces, 2 teaspoons garlic powder, 1 teaspoon oregano, and salt and pepper to taste; cook, stirring occasionally, until the chicken is mostly cooked through, about 5 minutes.
Add the sun-dried tomatoes and continue cooking until the chicken is fully cooked.
Stir in the dry orzo and toast it in the pot for 1–2 minutes, stirring so it browns lightly.
Pour in 1 quart chicken broth and stir, then bring to a gentle simmer.
Simmer, uncovered, for 10–15 minutes or until the orzo is tender and has absorbed most of the liquid, stirring occasionally to prevent sticking.
Remove from heat and stir in the Boursin cheese and 1–2 cups fresh spinach until the cheese melts and the spinach wilts.
Taste and adjust seasoning with more salt and pepper if needed, then serve topped with the optional grated Parmesan.