Try Kindle Comic Converter. Despite its name, it works for all types of readers, and can output EPUB. Be sure to select the generic reader output, enable Color Mode, and select EPUB as the output format.
Since the CBZ format is not standardised, there are some pitfalls if you try to achieve this.
The best you can do is render the ToC as an image and add it at the front of list of image files contained in the CBZ.
Adding an extra file with the ToC information might break existing readers, if that ToC is not an image file.
An alternative is to load the data ...
When you open the conversion window, before actually starting the process, go to the comic input tab, you will find a box labeled change images dimensions1.
By default, Calibre uses the settings from the page setup tab to select standard output settings for the selected device, this includes that device screen size, to which the images are resized.
While many desktop readers have this feature, I own a Kobo Glo and this option doesn't seem to be available.
As you probably already know, CBZ and CBR files are just plain standard zip and rar archives with renamed extension. On their inside, the comic pages are numbered image files, which the reader simply shows to you in alphabetical order.
So, in example ...