Preheat your grill or a grill pan over medium-high heat.
In a small bowl, mix together olive oil, garlic powder, onion powder, oregano, paprika, salt, and pepper. Rub this mixture all over the chicken breasts.
Grill the chicken for 6-7 minutes on each side, or until fully cooked and internal temperature reaches 165°F. Remove from heat and let rest for 5 minutes before slicing.
While the chicken is resting, prepare the tzatziki sauce. In a medium bowl, combine Greek yogurt, grated cucumber, minced garlic, olive oil, lemon juice, and salt. Mix well and refrigerate until ready to serve.
To assemble the bowls, divide the cooked quinoa among four bowls. Top with sliced chicken, cherry tomatoes, cucumber, red onion, olives, and parsley.
Drizzle each bowl with tzatziki sauce before serving.