Slice Chicken: Slice both chicken breasts right through the centre to create 4 even-sized breasts.
Marinade: In a medium-sized mixing bowl combine yoghurt, lemon juice, red wine vinegar, extra virgin olive oil, oregano, garlic, salt & pepper.
Marinate Chicken: Toss the chicken in the marinade until evenly coated. Cover and marinate in the fridge for a minimum of 2 hours (up to 24 hours). Take out the fridge around 30mins before needed, just so you're not frying cold chicken.
Cook Chicken: Lightly brush a griddle pan with oil (~1/2 tbsp) and bring to medium-high heat. Fry the chicken breasts on both sides until lightly charred and cooked right through the centre, working in batches if you need to (3-4mins each side depending on thickness). Rest to one side for 5-10mins, then slice into strips.
Salad: In a large mixing bowl whisk together extra virgin olive oil, red wine vinegar, oregano, salt and pepper. Toss in red onion, olives, feta, tomato, cucumber and pepper.
Serve: Add the salad to a large serving plate and rest the sliced chicken on top. Add a pinch of oregano then serve immediately with flatbreads!