In a mixing bowl, combine olive oil, lemon juice, minced garlic, oregano, salt, and pepper. Add chicken breasts and marinate for at least 30 minutes.

Preheat the grill to medium-high heat. Remove chicken from marinade and discard the marinade.

Grill chicken for 6-7 minutes on each side or until cooked through and juices run clear.

In a saucepan, bring water to a boil. Add quinoa, reduce heat to low, cover, and simmer for 15 minutes until water is absorbed.

Fluff quinoa with a fork and let cool.

In a large bowl, combine cooled quinoa, cherry tomatoes, cucumber, red onion, feta cheese, and parsley.

Drizzle with lemon juice and olive oil, then season with salt and pepper. Toss to combine.

Slice grilled chicken and serve over a bed of quinoa salad.