Rinse quinoa and combine with water in a saucepan; bring to a boil, then reduce heat and simmer covered for 15 minutes until liquid is absorbed.
In a bowl, toss chicken cubes with 1 tablespoon olive oil, oregano, garlic powder, salt, and pepper.
Heat remaining olive oil in a skillet over medium-high heat; cook chicken for 8-10 minutes until internal temperature reaches 165°F (74°C).
Prepare tzatziki by mixing Greek yogurt, minced garlic, lemon juice, and dill in a small bowl; season with salt and pepper.
Assemble bowls by layering cooked quinoa, grilled chicken, cucumbers, tomatoes, red onion, and olives.
Top with crumbled feta cheese and a generous dollop of tzatziki sauce before serving.