In a medium saucepan, combine the rinsed quinoa and 2 cups of water. Bring to a boil over medium-high heat.
Once boiling, reduce heat to low, cover, and simmer for 15 minutes or until the quinoa is tender and water is absorbed.
Remove the quinoa from heat and let it sit covered for 5 minutes. Fluff with a fork and set aside to cool slightly.
While the quinoa cooks, season the chicken breasts with 1/2 teaspoon salt and 1/4 teaspoon black pepper.
Heat 1/2 tablespoon olive oil in a large skillet over medium heat.
Add the chicken breasts and cook for 6-7 minutes per side or until fully cooked and internal temperature reaches 165°F (74°C).
Remove the chicken from the skillet and let it rest for 5 minutes, then dice into bite-sized pieces.
In a large bowl, combine the cooked quinoa, diced chicken, cherry tomatoes, cucumber, red onion, parsley, and feta cheese.
In a small bowl, whisk together the remaining 1/2 tablespoon olive oil, lemon juice, Dijon mustard, minced garlic, 1/4 teaspoon salt, and 1/8 teaspoon black pepper until well combined.
Pour the dressing over the quinoa salad and toss gently to combine all ingredients evenly.
Serve immediately or refrigerate for up to 2 days for flavors to meld.