Heat olive oil and 1 tablespoon of butter in a large deep skillet or Dutch oven over medium-high heat.
Season chicken with salt and pepper, then sear until browned and cooked through (6-8 minutes). Remove chicken from pan and set aside.
Add the remaining tablespoon of butter to the pan. Sauté onion, carrots, and celery for 5 minutes until softened.
Add minced garlic and dry orzo pasta. Toast the orzo for 2 minutes, stirring constantly until lightly golden.
Deglaze the pan with chicken stock and stir in dried thyme. Bring to a boil, then reduce heat to a simmer.
Cook uncovered for 10-12 minutes, stirring frequently to release starches, until orzo is al dente and liquid is mostly absorbed.
Stir in the cooked chicken, frozen peas, and heavy cream. Simmer for 2-3 minutes until the sauce has thickened and coated the pasta.
Remove from heat, garnish with fresh parsley, and adjust seasoning to taste before serving.