In a medium bowl, make the chicken marinade: Whisk together olive oil, lemon juice, minced garlic, oregano, salt and pepper.
Add the chicken to the marinade and evenly coat; cover and allow to marinade for 30 minutes or overnight in the refrigerator.
While chicken is marinating, prepare the yoghurt sauce: combine all the Tzatziki sauce ingredients in a bowl and mix well. Cover and refrigerate until ready to serve.
In a large bowl, add cucumber, tomatoes, pepper, olives, onion, cheese and dill. Stir well to combine then arrange the salad on a large platter or 4 small bowls.
Heat a large skillet over medium-high heat. Remove the chicken from the marinade and add to the pan.
Cook for about 5-6 minutes each side, or until the chicken is tender and cooked through.
Remove chicken from the pan; allow to rest for 5 minutes. Slice thickly and add it to the salad.
Serve the salad with the Tzatziki sauce.