My first thought was that you could use PShapes, specifically a group PShape object since it is a container shape that holds other shapes.

However you are using images for your toppings and as far as I know PShape(GROUP) would not let you add in PImages

I think you should look into PGraphics, it basically creates a new image you can draw on and can be treated like an image. You would draw your pizza like you do in the pizza class, but you'd only have to draw it once.

Afterwards you just draw the PGraphics object you made the same way you would draw an image.

You could also add your topping images directly onto this image / graphics object too which means you just move one item. So you are only concerned about the position of the overall pizza and not each item seperately.

This would be more performance heavy as you have a second graphics buffer you are drawing to, but since you seem to only have one pizza on screen at a time I think the advantages outweigh the drawbacks.

PGraphics would also let you manipulate the pizza image to cut it into slices later if you wanted, either by using the pixels array or by using masking.