In a large mixing bowl whisk together the olive oil, lemon juice, garlic and dried mixed herbs with a little salt and milled pepper. Toss the sweet potato, leek and mushrooms in the dressing, then place the veg in a roasting tin.
Now toss the chicken pieces in the remaining dressing and place amongst the vegetables and bake for 15 minutes.
Whilst the chicken is cooking, make the herby crumb by simply popping the ciabatta, parsley and lemon zest into a food processor and whizzing until you have a rough crumb.
Now remove the tray from the oven, add the mushrooms and cherry tomatoes to the tray, scatter over the herby crumb and pop back into the oven for a further 10-15 minutes. Serve straight away.