In a bowl, combine olive oil, garlic powder, onion powder, paprika, oregano, salt, and pepper. Add the chicken breasts and coat evenly. Let marinate for at least 30 minutes.
While the chicken is marinating, prepare the tzatziki sauce by mixing the Greek yogurt, lemon juice, dill, and a pinch of salt in a small bowl. Set aside in the refrigerator to chill.
Heat a grill pan or skillet over medium-high heat. Cook the marinated chicken for about 6-7 minutes per side, or until fully cooked and no longer pink in the center. Remove from heat and let rest for a few minutes before slicing.
In serving bowls, layer the cooked rice, sliced chicken, diced cucumber, cherry tomatoes, and red onion.
Drizzle the tzatziki sauce over the top and serve immediately.