Turn their country to glass and DO NOT rebuild it.
There’s a lot of Iranians who despise the theocrats running the country. No need to kill them along with the ones that really do need to get whacked. Target power plants, substations, oil refineries and loading facilities and the end comes pretty quickly. Initial attack would be with cruise misseles and then B-2 strikes when air defenses have been suppressed. Take maybe 3 days.