Heat olive oil in a large skillet or Dutch oven over medium-high heat. Add the diced onion and cook for 2-3 minutes until softened. Stir in the minced garlic and cook for another minute until fragrant.

Add the chicken pieces to the skillet. Season with Italian seasoning, salt, and pepper. Cook, stirring occasionally, until the chicken is golden brown and cooked through, about 5-7 minutes. Remove the chicken and set aside.

Add the uncooked orzo to the same skillet. Stir constantly for about 1 minute until it's lightly toasted.

Pour in the chicken broth, making sure to scrape up any browned bits from the bottom of the pan. Bring to a simmer, then reduce the heat to low, cover, and cook for 10-12 minutes, until the orzo is nearly al dente.

Stir the broccoli florets and the cooked chicken back into the skillet. Cover and continue to cook for another 3-5 minutes, until the broccoli is tender and the orzo is fully cooked.

Remove the skillet from the heat. Stir in the shredded cheddar and Parmesan cheese until melted and the sauce is creamy. Season with additional salt and pepper if needed. Serve immediately.