Season both sides of the chicken thighs with the garlic powder, thyme, and Cajun seasoning.
Heat the olive oil in a large skillet over medium heat. Add the chicken thighs and cook for 5 to 6 minutes per side, or until golden brown and the internal temperature reaches 165°F. Transfer the chicken to a plate and set aside.
Add the onion, celery, and bell pepper to the same skillet. Cook for 5 to 7 minutes, stirring occasionally, until softened.
Stir in the tomato paste and cook for 1 minute, stirring constantly, until fragrant.
Pour in the chicken broth, scraping up any browned bits from the bottom of the skillet. Bring the mixture to a gentle simmer.
Stir in the orzo. Cook for 10 to 12 minutes, stirring frequently, until the orzo is tender and most of the liquid has been absorbed.
Reduce the heat to low and stir in the half-and-half and remaining 1 teaspoon Cajun seasoning, if desired. Cook for 1 to 2 minutes until creamy and heated through.
Return the chicken to the skillet and cook for 2 to 3 minutes, or until warmed through.
Top with freshly grated Parmesan cheese and parsley before serving.