Combine olive oil, lemon juice, minced garlic, salt, and pepper in a bowl and coat the chicken breasts with the mixture. Let them marinate for 10 minutes to soak in the flavors.
Warm a large skillet over medium heat and cook the chicken for 5 to 6 minutes on each side until browned and cooked through with clear juices.
Add the rinsed quinoa to the skillet and stir continuously for around 2 minutes until the grains become fragrant and slightly golden.
Pour in the chicken broth carefully, bring the mixture to a boil, then cover and reduce the heat to low. Let it simmer for 15 minutes until the quinoa is tender and the liquid has evaporated.
Place the cooked chicken breasts back on top of the quinoa in the skillet. Cover again and let rest for 5 minutes to allow flavors to meld.
Serve the dish warm, garnished with fresh parsley, cherry tomatoes, and optional red pepper flakes for an extra kick.