Deseed the peppers and tear into big chunks, peel and quarter the onions and break apart into petals, then place it all in a 30cm x 40cm roasting tray.
Use a large sharp knife to carefully cut down the back of the chicken, so you can open it out flat, then score the legs. Add to the tray with the harissa, and a little sea salt, black pepper and red wine vinegar. Toss well, making sure you get into all the nooks and crannies of the chicken.
Sit the chicken flat on top of the veg, skin side up, and roast it all for 50 minutes, or until gnarly and cooked through. Pick over the mint leaves before dishing up.