Heat olive oil in a large deep skillet or Dutch oven over medium-high heat.
Add the chicken pieces and cook for 5-6 minutes, stirring occasionally, until browned and cooked through. Remove chicken from the pan and set aside.
In the same pan, add the chopped onion and cook for 3 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Add the orzo pasta to the pan and stir to coat with the oil, onion, and garlic mixture.
Pour in the chicken broth, and season with salt and black pepper. Stir to combine.
Bring the mixture to a boil, then reduce heat to medium-low, cover, and simmer for 10 minutes, stirring occasionally to prevent sticking.
After 10 minutes, stir in the cooked chicken, cherry tomatoes, and baby spinach.
Cover and cook for another 5 minutes, until the orzo is tender and the spinach is wilted.
Remove from heat and stir in the basil pesto and grated Parmesan cheese until well combined.
Serve immediately, garnished with additional Parmesan if desired.