In Italian the “ce” and “ci” are always pronounced with a “ch” sound as in “children” – “che” and “chi,” respectively. So “vermicelli” is pronounced ver-mi-chel-li.
(But to confuse things, in Italian “che” is pronounced “ke” and “chi” is pronounced “ki”. “Bruschetta” is pronounced “Bru-sket-ta”.)
There is no other way to pronounce these four letter combinations unless you’re getting into dialects.
And since I’m here, the “sci” and “sce” combinations are pronounced “shi” and “she”, so Steve Buscemi’s last name would be pronounced in Italian “Bu-she-mi” (I don’t know how he himself pronounces it).