Marinate the Chicken
In a bowl, mix Greek yogurt, olive oil, lemon juice, garlic, oregano, cumin, salt, and pepper. Coat the chicken and marinate for at least 30 minutes (or up to 24 hours for deeper flavor).
Cook the Quinoa
In a saucepan, combine rinsed quinoa and water or broth. Bring to a boil, reduce heat, cover, and simmer for 15 minutes, or until the liquid is absorbed. Fluff with a fork and set aside.
Grill or Sauté the Chicken
Heat a grill or stovetop skillet over medium-high heat. Cook the chicken for 5-7 minutes per side until fully cooked and slightly charred. Let it rest for 5 minutes, then slice into strips.
Assemble the Bowls
Divide the cooked quinoa into bowls. Top with sliced chicken, cherry tomatoes, cucumber, red onion, Kalamata olives, and feta cheese.
Garnish and Serve
Drizzle with tzatziki sauce, garnish with fresh parsley or dill, and serve with lemon wedges for extra flavor.