01 - Whisk together olive oil, lemon juice and zest, minced garlic, chopped parsley, oregano, thyme, salt, and black pepper in a mixing bowl. Add chicken breasts, coat thoroughly, cover, and refrigerate to marinate for at least 15 minutes or up to overnight.
02 - While chicken marinates, bring water or low-sodium chicken broth to a boil in a medium saucepan. Add rinsed quinoa, reduce heat to low, cover, and simmer for 15 minutes or until liquid is fully absorbed. Remove from heat, fluff quinoa with a fork, and set aside to cool.
03 - Preheat grill or grill pan over medium-high heat. Place marinated chicken breasts on the grill and cook for 6 to 7 minutes per side, or until the internal temperature reaches 165°F and juices run clear. Transfer to a board and allow to rest for 5 minutes, then slice.
04 - In a large mixing bowl, combine cooled quinoa, halved cherry tomatoes, diced cucumber, finely chopped red onion, crumbled feta cheese (if using), chopped parsley, and mint.
05 - In a separate bowl, whisk together olive oil, lemon juice, Dijon mustard, minced garlic, honey, and salt and pepper until fully emulsified.
06 - Pour prepared dressing over the quinoa and vegetable mixture; toss gently to coat all ingredients evenly.
07 - Arrange sliced grilled chicken on top of the salad and serve immediately or refrigerate to chill before serving.