Une tranche de pizza?
Why is it "de pizza" and not "de la pizza"?
As we're apparently not talking about a specific pizza. Otherwise it would have been 'slice of the pizza'
When do you use "un morceau" and when "une part" ??
In Quebec, "slice of pizza" is often translated as "pointe de pizza".
"portion de pizza" would be a relatively geographically and dialectologically versatile way of indicating "slice of pizza".
How would this sentence work with "avoir envie de"?
"Qui a envie d'une part de pizza?"
Alternatively:
"Y a-t-il quelqu'un parmi vous qui aurait envie d'une part de pizza?" (Might any of you feel like a slice of pizza?).
"Do you feel like having a slice of pizza?" could also be translated as:
"Ça te tente d'avoir une part de pizza?".