In a mixing bowl, combine olive oil, minced garlic, dried oregano, ground cumin, salt, and pepper. Add the chicken breasts, ensuring they are thoroughly coated in the marinade. Cover the bowl and let it sit in the refrigerator for at least 30 minutes, or up to overnight for deeper flavor.

Preheat your grill or skillet over medium-high heat. Cook the marinated chicken for about 6-7 minutes on each side until it achieves an internal temperature of 165°F. Remove the chicken from heat and let it rest for 5 minutes to allow the juices to redistribute before slicing it thinly.

In a small bowl, whisk together the plain Greek yogurt and freshly squeezed lemon juice until smooth. Adjust with extra lemon if desired.

In a separate mixing bowl, combine diced tomatoes, diced cucumber, sliced red onion, chopped Kalamata olives, and crumbled feta cheese. Toss gently until well mixed.

In a dry skillet over medium heat, warm the corn tortillas for about 30 seconds on each side until pliable and slightly toasted.

Take each warmed tortilla and layer sliced grilled chicken evenly in the center. Top with the fresh salad mixture and drizzle with the zesty yogurt sauce. Garnish with chopped parsley.