The soft C = TH really only exists when you’re talking about ZI/CI or ZE/CE
That sound is sometimes known as “theta” which is funny because la zeta is “the letter Z” OR “the Greek letter Theta”.
it’s because ZI an ZE rarely exist in Spanish; el zinc / el cinc = Zinc; el zirconio / el circonio = Zirconium (Zr).
The soft C is not totally common; many places use el seseo which is to treat it as an S sound.
ZA, ZO, and ZU are pronounced fully (usually as an S) - empezar, perezoso/a, azul.
But when dealing with loanwords or foreign names, Spanish does its best to imitate the language it came from. That’s known as voz ___…
So voz francesa “French voice” would be for words taken from French el / la chef, el rendez-vous, glacé = “glazed / frosted” (instead of glaseado), etc.
And voz inglesa “English voice” would be for words taken from English… el kiosk, el récord, el / la Internet etc.
In this case la pizza would be pronounced with a full Z to mimic la voz italiana “Italian voice”.