How it works
Add 〜たい (want to) to a verb stem to say you want to do something: 食べる (eat) becomes 食べたい (want to eat). There's no polite です (is) or ます (polite) here, so it sounds casual — like thinking out loud. In speech like this the object particle を (object) after ピザ (pizza) is simply dropped.
hanamaru