Prepare the Chicken: If using chicken breasts, gently pound them to an even thickness of about 1.5-2 cm. This ensures even cooking and prevents drying out. You'll hear a satisfying rhythmic thud as the mallet meets the chicken, creating a uniform canvas for the marinade.

Whisk the Marinade: In a medium-sized bowl, combine the olive oil, apple cider vinegar, lemon juice, Worcestershire sauce, smoked paprika, garlic powder, onion powder, dried oregano, black pepper, sea salt, and cayenne pepper (if using). Whisk vigorously until all the spices are well incorporated and the mixture emulsifies slightly, taking on a uniform, slightly reddish-brown hue and emitting a wonderfully aromatic, tangy, and smoky scent.

Marinate the Chicken: Place the chicken pieces into a large, resealable bag or a shallow dish. Pour the prepared marinade over the chicken, ensuring every piece is thoroughly coated. Seal the bag, pressing out as much air as possible, or cover the dish. Refrigerate for a minimum of 2 hours, but for the best flavour and tenderness, allow it to marinate for 4 hours. You'll notice the chicken absorbing the rich marinade, its surface beginning to deepen in colour and texture.

Preheat the Grill: About 15 minutes before you’re ready to cook, preheat your outdoor grill or indoor griddle pan to a medium-high heat (around 200°C / 400°F). Lightly oil the grates or pan to prevent sticking. You'll see wisps of smoke and feel the radiant heat building, signalling it's ready to sear.

Grill the Chicken: Remove the chicken from the marinade, allowing any excess to drip off (do not wipe it clean, as that's where the flavour is!). Discard the remaining marinade. Place the chicken pieces onto the hot grill. Grill for 6-8 minutes per side, depending on the thickness of your chicken. Look for beautiful, dark grill marks forming, a golden-brown crust, and listen for the satisfying sizzle as the chicken cooks.

Check for Doneness: The chicken is cooked through when it reaches an internal temperature of 74°C (165°F) with a meat thermometer inserted into the thickest part. The flesh should appear opaque white throughout, with no pink remaining. When you press it gently, it should feel firm yet springy, and emit a wonderfully cooked, slightly charred aroma.

Rest the Chicken: Once cooked, transfer the grilled chicken to a clean plate or cutting board. Tent it loosely with foil and let it rest for 5-10 minutes. This crucial step allows the juices to redistribute throughout the meat, ensuring maximum tenderness and moisture. You'll notice the chicken looking even more plump and inviting after resting.

Serve: Garnish with fresh parsley, if desired, and serve immediately.