its called the Dragon Sicillian and you pawn storm on the queen side in responce, who ever is fastest wins. (its more complicated than that, but that is the extremely short version abridged and reduced into a snippet that cohesively summarizes the idea
K-Side Pawn Rush

Opposite side castling can happen in many different openings.
Try to open lines and create threats anywhere else on the board and avoid moving the pawns in front of your king (which makes their attack faster and weakens your king in general).
Sometimes you attack their king and sometimes you try to get play in the center. As a last resort you fall back on passive defense and just try defending your castled king without getting any active play of your own.

yeah that is a more detailed version.
And the version that doesn't make up which opening it is for no apparent reason.

I was kind of joking with sicillian Dragon because there it is common place for that to happen, KID, I face it playing the Dutch, it can happen in the Spanish Game, it can happen in any line, its just its more common in some.

sometimes you can wait till the opponent's pawn gets all the way in front of your king then not take it back and use it against them as a shield : )
i also like to try to exploit the holes created as they push their pawns, sometimes you can lodge the queen or bishop or such in there : ) amidst their advancing pawn holes : )
How do you handle a player who castles Q-side and then rushes your K-side castled position with pawns?
(Be nice.)