Score and butterfly the chicken fillet to ensure they will cook rapidly and uniformly.
Next, in a bowl, pour the buttermilk, garlic, lemon zest and juice, herbs, salt and pepper. Combine well. Add the chicken fillets and set aside in the refrigerator for 1 hour or up to a day to marinate.
Once, ready to cook, preheat a griddle pan or barbecue. Drizzle the potatoes with some oil and Place on the griddle pan. Cook over low heat until warmed through and coloured on the edge. Then, add the chicken fillet and cook for 3-5 minutes on each side until fully cooked through, depending on the thickness of the chicken fillets. Season well.
Remove from the griddle and set aside on a board for a minute or so. Carve if desired. .
Place the salad leaves on a serving platter and add the cooked potatoes. Drizzle with some olive oil and a drizzle of lemon juice, salt, and pepper. Add the carved chicken fillets and serve immediately.