Prep: Place each chicken breast in a large zip-top storage bag. Using a meat mallet or rolling pin, pound to an even ½-inch thickness.
Marinate the chicken: Combine the olive oil, lemon juice, garlic, thyme, oregano, salt and pepper in a small bowl and whisk until combined. Pour the marinade in the bag with the chicken and turn to coat. Place the bag in a baking dish (in case it leaks) and place it in the fridge.
Cook: Rinse the quinoa cold water in a fine mesh sieve. Place the quinoa and 2 ¼ cups water in a medium saucepan. Bring the water to a boil, then reduce to a simmer. Cover and cook until the quinoa is tender and the water has been absorbed, about 10 to 15 minutes. Set aside to cool.
Grill: Preheat your grill to medium-high heat, around 400 – 450°F. The grill needs to be hot when you add chicken, allowing it to sear and cook evenly. Remove the chicken from the marinade and discard excess. Grill the chicken for 5-7 minutes each side (depending on thickness) until cooked through and the internal temperature reaches 165°F/75°C. Remove the chicken and let it rest for 5 minutes. Slice the chicken into strips.
Assemble: Divide the quinoa evenly among four serving bowls. Top each bowl with the chicken, then add cucumber, tomatoes, avocado, red onion, feta cheese, and Kalamata olives. Serve as is or with Greek yogurt or Tzatziki sauce!
