In a bowl, combine olive oil, minced garlic, dried oregano, ground cumin, salt, and pepper until well mixed. Add the chicken breasts, ensuring they are coated thoroughly with the marinade. Cover the bowl and let the chicken marinate in the refrigerator for at least 30 minutes, allowing the flavors to infuse.

Preheat your grill or skillet to medium-high heat, about 375°F. Once hot, add the marinated chicken breasts and cook for 6-7 minutes on each side, or until cooked through and the internal temperature reaches 165°F. The chicken should be golden brown and juicy. Remove from heat and let it rest for a few minutes before slicing.

In a small bowl, whisk together plain Greek yogurt and freshly squeezed lemon juice until smooth and creamy. This tangy yogurt sauce will brighten your Mediterranean Chicken Tacos. Set the sauce aside to let the flavors meld while you prepare the remaining toppings.

In a mixing bowl, combine diced tomatoes, cucumber, red onion, Kalamata olives, and crumbled feta cheese. Toss the mixture gently to combine, ensuring that the vegetables are evenly distributed. This fresh salad topping will add vibrant color and crunch to your Mediterranean Chicken Tacos.

Heat a dry skillet over medium heat and add corn tortillas one at a time, warming them for about 30 seconds on each side. The tortillas should become pliable and slightly toasted. This step enhances their flavor and prepares them for a cozy embrace around the filling.

On each warmed tortilla, place a few slices of grilled chicken. Carefully add a generous spoonful of the salad mixture on top, followed by a drizzle of the yogurt sauce. For a beautiful finish, sprinkle fresh parsley over the tacos. Serve immediately to enjoy the fresh flavors of your Mediterranean Chicken Tacos!