Simon Grimm, an Ionic Developer Expert, provides a detailed tutorial on implementing navigation within Ionic modals using the ion-nav component, a solution for handling navigation in overlays that are not part of standard Angular routing. The tutorial outlines the process of starting with a blank Ionic app, creating a custom navigation component with ion-nav, and using it to establish a navigation stack within a modal. Simon explains how to present the modal and integrate navigation functionality, including responding to Android's back button by setting up a handler to manage navigation actions. This approach allows users to navigate within modals independently of the app's URL routing, offering flexibility for complex navigation scenarios. The tutorial also emphasizes the benefits of using Capacitor's livereload feature for testing on devices and promotes further learning resources available through the Ionic Academy.