Begin by dicing the boneless chicken breasts into bite-sized pieces and seasoning them generously with Cajun seasoning. In a large pot or Dutch oven, heat 1 tablespoon of olive oil over medium-high heat. Once shimmering, add the chicken and sear for about 5-7 minutes, until golden brown and cooked through. Remove the chicken from the pot and set aside, leaving the juices for the next steps.

In the same pot, lower the heat to medium and add the diced onions. Sauté for about 3 minutes, stirring occasionally until softened and fragrant. Next, add the minced garlic and (if using) diced bell pepper to the pot. Continue to sauté for another 2-3 minutes, allowing the vegetables to become tender and aromatic.

Stir in 1 ½ cups of orzo pasta along with 4 cups of chicken broth. Increase the heat to bring the mixture to a simmer. Once bubbling, reduce the heat to low, cover the pot, and let it cook for 10-12 minutes.

Remove the pot from the heat and slowly stir in 1 cup of heavy cream and 1 cup of grated Parmesan cheese. Mix until the cheese has melted completely and the sauce is creamy and smooth.

Gently fold the seared chicken back into the pot, ensuring it's evenly distributed throughout the dish. Season with salt and pepper to taste. Garnish with fresh parsley if desired and serve immediately.