There are plural and singular, but in most cases the singular is used.

Oxford Advanced English-Chinese Learning Dictionary

pizza

/_ pi _ ts _； Italian pie (usually round) with tomatoes, cheese, anchovies, etc., and Italian scones (with tomatoes, cheese, etc.). And baked in an oven).

Additional examples:

Ahamandsmushroom pizza◆ Is that thereanypizzaleft?

pizza

Pizza example:

Hello, I want to order a cheese pizza.

Hello, I want to order a large cheese pizza.

Let's go eat pizza.

Let's go out for a big pizza!

Five minutes.

It takes 5 minutes to knead the pizza dough.