I found some pizzalicious origami. It's hard to believe, but all of these things are made out of folded paper!
This classic pepperoni slice is from Gilad's Origami Page. Instructions can be found in the Origami USA 2003 convention book.
This origami tomato plant is from Graphic Content.
This Mushroom is from Diagrami.
This onion/garlic is from Toxel.
This could be a slice of Chicago syle deep dish if you used the right paper. You can get the PDF tutorial on how to make it from lilblackdog's Etsy page.
Here is some basil for your pie from Joost Langeveld Origami.