Scatter the onions or shallots, potatoes, carrots and parsnips in a large, sturdy roasting pan. Drizzle with the oil and shake the pan so that the vegetables are coated in oil. Sprinkle with salt and pepper and roast in a preheated oven, 190°C (375°F), Gas Mark 5, for 30 minutes until beginning to colour.
Add the courgettes and rosemary sprigs to the pan and toss the vegetables together. Return to the oven for a further 10 minutes.
Mix together the mustard, maple syrup and a little salt. Tuck the pork chops among the vegetables and brush with about half the maple glaze. Return to the oven for 20 minutes.
Turn the pork chops over and brush with the remaining maple glaze. Return to the oven for a further 15 minutes or until the chops are cooked through.