Most likely from the spanish word "bulla" (pronounced boo-ya) meaning "racket" (in the sense of a lot of noise).
Earliest documented use of the word thus far: Used by the Latino hip-hop group Cypress Hill on the album Cypress Hill, which was released on August 13, 1991.
Originally used in the same way as "BANG! GOTCHA!", the definition has expanded with popularity and is most commonly used as an exclamation of triumph, in the same way as "Gotcha," or "So there!" or "Hah!".
Partial Lyric from "Hole in the Head" by Cypress Hill
Madman gonna get cha, quick with the cuente
See a gang, no there ain't no jugete
Rollin like a pyscho with the windows rolled down
Who you lookin at, you tryin to fade me clown?
Plato, si mon, you want static
When you reach for your gat to load your automatic
(Boo-yaa!!) Spittin out buckshots
Homey say blood claat, so you can call a pig
Cause no one could handle, I wind up, and loco
Insane in the brain, you get the bullet and