Check out this collection of animated hamburgers. All set up to work out of the box with the mmenu.js plugin. Click a hamburger to see the animation (and make sure the menu on the left is closed).
The mburger.css and mburger.js files are licensed under the Creative Commons Attribution 4.0 International license. You can use it in all your personal, non-commercial and commercial projects.
Install with NPM:
npm install mburger-css
Download directly from the Github repository.