Place the lamb, fat side down on a microwave oven roasting rack or on top of an inverted saucer set in a glass baking dish.
Place the bread, parsley, and rosemary in a blender and blend until finely chopped.
Spread the mixture on the surface of the lamb.
Heat the butter and garlic in a custard cup on the highest setting for 40 seconds. Drizzle the garlic butter over the lamb.
Cook the lamb on the highest setting for 10 minutes.
Rotate the dish one-quarter of a turn and cook on "roast" setting for 8 min utes.
Season with salt and pepper and leave to rest for 10 minutes before slicing.