Cut open the breast side of the chicken and flatten it out by pressing down hard (it will then look like a large toad).
For the marinade, peel and chop the garlic. Combine all of the marinade ingredients: garlic, mustard, honey, oregano, olive oil.
Lay the chicken down in a dish, spread over this marinade (on both sides), season, cover with plastic wrap, chill for 24 hours.
Place the chicken over gentle heat, and cook it for 45 minutes, turning from time to time. Once the chicken is cooked, scatter with chopped parsley and spring onions and cover for 2 minutes so they soften. Serve immediately.