In a mixing bowl, whisk together olive oil, lemon juice, minced garlic, oregano, cumin, salt, and black pepper until well combined. This mixture will infuse the chicken with Mediterranean flavors.

Add the chicken breasts to the marinade, ensuring they are well coated. Cover the bowl with plastic wrap and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.

Preheat the grill to medium-high heat (about 375°F to 400°F). This ensures a good sear on the chicken.

Remove the chicken from the marinade and discard any leftover marinade. Place the chicken on the grill and cook for 6-7 minutes on each side, or until the internal temperature reaches 165°F. Use a meat thermometer to check for doneness.

Once cooked, remove the chicken from the grill and let it rest for 5 minutes. This allows the juices to redistribute, keeping the chicken moist.

Slice the grilled chicken into thin strips. This makes it easier to fit into the tortillas and allows for more even distribution of toppings.

Warm the tortillas on the grill for about 30 seconds on each side, or until pliable.

To assemble, place a few strips of chicken in the center of each tortilla. Top with chopped romaine lettuce, halved cherry tomatoes, crumbled feta cheese, sliced red onion, and a drizzle of tzatziki sauce.

Garnish with fresh parsley for added flavor and color.