Heat the oil in a roasting tin on the hob (use 2 rings), then add the onions, pears, most of the rosemary and seasoning. Fry for 5 mins or until just starting to caramelise.
Heat grill to high. Season the pork, then arrange among the veg and fry for 5 mins, turning halfway until golden and cooked
through. Scatter with the remaining rosemary and the cheese, grill until the cheese starts to melt, then serve.