Of course, the word voila properly pronounced in French sounds a bit like "vwalla", but with the "v" in front pronounced softly, almost like an "f". Being stupid Americans though, they can't pronounce anything which doesn't sound 100% English (not that they can pronounce English either) so in their incredibly lazy way, they don't even try to pronounce it correctly.
So I was on a cruise around the world and we were heading towards American territory again. This lady on the ship asked me who the stupidest people in the world are. So I pointed at America and said "Walla!"
Hamoody:I did, walla i did!
Ahmed: Yea walla he did.
Hassan: Thats bullshit! Walla u didn't
Hamoody: Walla i did, cuz ill kill you in b-ball too!
"Walla" is a word used by ignorant people (particularly Americans) who simply don't know any better.