In a bowl, combine olive oil, oregano, garlic powder, paprika, salt, and pepper. Add the chicken breasts and coat them well with the marinade. Cover and let it marinate in the fridge for at least 30 minutes or up to 2 hours for more flavor.
Preheat a grill or a skillet over medium-high heat. Cook the marinated chicken for about 5-7 minutes on each side until cooked through and the internal temperature reaches 165°F (75°C). Once cooked, let the chicken rest for a few minutes before slicing it into thin strips.
In a bowl, mix Greek yogurt, grated cucumber, minced garlic, lemon juice, salt, and optional dill. Stir until well combined. Adjust seasoning to taste and refrigerate until ready to serve.
Start with a base of quinoa or brown rice in each bowl. Top with sliced chicken, cherry tomatoes, diced cucumber, shredded lettuce, and red onion.
Drizzle tzatziki sauce over the top and sprinkle with crumbled feta cheese and chopped parsley if desired.
Serve immediately and enjoy your delicious Chicken Gyro Bowls!