First, the man creating the stuffed burrito defecates in his partner's mouth. The feces is considered "the beans" of the burrito.
Generally, the receiver will vomit a little bit, creating a mixture similar to pico de gallo or other salsas.
Third, the performer rotates his anus away from his partner's mouth and sticks his penis into the poop.
Upon climaxing, he shoots his semen into the crap-filled orifice, supplying the burrito's sour cream.