Crush cardamom seed in a mortar and pestle (or smash with flat bottom of a heavy glass).
Add pistachios and coarsely crush (or mince).
Cut or pull peel from mangoes and discard. Cut mangoes lengthwise, along each side of pit, to remove fleshy cheeks.
Slice fruit. Also slice remaining fruit from pit and discard pit. Arrange fruit on a platter.
Drizzle mangoes with honey, then sprinkle with cardamom mixture and nutmeg.