Thanks! For anyone reading this that wants to know exactly what I changed, I made the following changes:
In the constructor of my App class (App.xaml.cs):
MainPage = new MainPage();
Replaced with:
MainPage = new NavigationPage(new MainPage());
Code to go from MainPage.xaml to Settings.xaml:
Navigation.PushAsync(new Settings());
Code to return from Settings.xaml back to MainPage.xaml:
Navigation.PopToRootAsync();
I also added the following to the ContentPage element in my MainPage.xaml & Settings.xaml files (you may or may not want this):
NavigationPage.HasNavigationBar="False"
Thanks again, and hopefully this can help others as well!