Heat 1 tablespoon olive oil in a large nonstick skillet over medium-high heat until hot.
Toss the chopped chicken with 1 tablespoon pesto, then add the chicken to the skillet along with the chopped onion, sliced carrots, and quartered zucchini.
Sauté the chicken and vegetables for about 3 minutes, stirring occasionally.
Add the chopped red bell pepper, uncooked orzo, and minced garlic to the pan and cook 2 more minutes, stirring.
Stir in the crushed tomatoes, the remaining 2 tablespoons pesto, chicken broth, optional chicken bouillon, dried oregano, salt, black pepper, and red pepper flakes.
Bring the mixture to a simmer, then cover and reduce heat to medium-low. Simmer 8–12 minutes, stirring every 5 minutes to keep the orzo from sticking, until the orzo and vegetables are tender.
Stir in 1/2 cup freshly grated Parmesan until combined. Taste and adjust seasoning with additional salt and pepper if needed.
Serve garnished with extra freshly grated Parmesan and chopped fresh parsley, if desired.
