Whisk all marinade ingredients together in a small bowl until fully combined. Taste and adjust seasoning.
Pound chicken breasts to an even 2cm thickness if using breasts.
Place chicken in a large zip-lock bag. Pour marinade over. Massage to coat all surfaces. Seal.
Refrigerate for a minimum of 2 hours. Up to 24 hours maximum for lemon-based marinades.
Remove chicken from fridge 30 minutes before grilling.
Preheat grill to high heat for 10 to 15 minutes until genuinely hot.
Remove chicken from marinade. Let excess drip off but do not wipe clean.
Season lightly with extra salt and pepper on both sides.
Oil grill grates with a folded oiled paper towel held in tongs.
Place chicken on hot grill. Do not move for 5 to 6 minutes until it releases cleanly.
Flip once. Reduce to medium heat or move to cooler zone.
Cook a further 5 to 7 minutes for breasts or 4 to 5 minutes for thighs until internal temperature reaches 74°C (165°F).
Remove from grill. Rest on a clean plate for 5 minutes.
Slice against the grain if desired. Arrange on a serving platter.
Garnish with parsley and flaky sea salt. Squeeze lemon generously over the top. Serve immediately.