Heat olive oil in a large pot or deep skillet over medium-high heat.
Add the chicken pieces to the pot, season with salt and black pepper, and cook until browned on all sides, about 5-6 minutes. Remove the chicken from the pot and set aside.
In the same pot, add the chopped onion and cook until softened, about 3 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Pour in the orzo pasta and stir to coat it with the oil, onion, and garlic mixture.
Add the chicken broth and bring to a boil.
Reduce heat to medium-low, cover, and simmer for 8-10 minutes, stirring occasionally, until the orzo is tender and most of the liquid is absorbed.
Return the cooked chicken to the pot along with the basil pesto, grated Parmesan cheese, and halved cherry tomatoes.
Stir everything together gently until well combined and heated through, about 2-3 minutes.
Taste and adjust seasoning with salt and black pepper as needed.
Remove from heat and garnish with fresh basil leaves before serving.