Heat olive oil in a large skillet over medium-high heat. Season chicken with salt and pepper, then cook 4-5 minutes per side. Remove and set aside.
Add butter to the same skillet, sauté garlic for 1 minute. Cook carrots and celery for 3 minutes. Stir in quinoa, thyme, and red pepper flakes.
Pour in chicken broth, bring to a boil. Return chicken on top, cover, and simmer 15 minutes until cooked through. Stir in spinach until wilted, then garnish with parsley.
Notes
Ensure chicken reaches an internal temperature of 165°F for safety.