Heat the oven: Heat the oven to 200 degrees C (180 degrees C fan). Put a large roasting tray in the oven while it heats. A hot tray helps the vegetables start crisping straight away.
Season everything: Put the potatoes, carrots, and onion in a large bowl with half the olive oil, half the salt, the pepper, and the oregano, and toss until coated. Pat the chicken dry, rub it with the remaining oil and salt, and season well on both sides.
Build the tray: Take the hot tray out, spread the vegetables in a single layer, and nestle the chicken pieces among them, skin side up. Tuck in the garlic halves, lemon slices, and herb sprigs, and pour the seasoned oil left in the bowl over the top.
Roast: Roast for 40 to 45 minutes, turning the vegetables once halfway if you remember. The chicken is ready when the skin is crisp and golden, the meat is cooked through, and the potatoes are soft inside with crisp edges. If the chicken browns faster than the vegetables soften, cover loosely with foil for the last 10 minutes.
Rest and serve: Rest the tray for 5 minutes, squeeze the roasted lemon wedges over it, scatter over the parsley, and serve straight from the tray. The soft roasted garlic can be squeezed out onto the chicken or potatoes. It is sweet and mild after roasting in the oven.