Marinate the Chicken
In a bowl, combine 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).
Cook the Chicken
Heat a grill or 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 rice or quinoa into bowls. Top with sliced chicken, cherry tomatoes, cucumber, red onion, Kalamata olives, and feta cheese.
Add the Finishing Touches
Drizzle with tzatziki sauce, garnish with fresh parsley or dill, and serve with warm pita wedges if desired.