.NET: Roslyn Has a Missing Path

This error seems to occur when I am opening an upgraded web project in Visual Studio 2019: 

  

This happens when the current codebase is using older VS2015 templates. 

The simplest approach is to open NuGet's Package Configuration Console in Visual Studio and enter the following to upgrade the compiler: 

Update-Package Microsoft.CodeDom.Providers.DotNetCompilerPlatform -r 

REFERENCE:  

https://stackoverflow.com/questions/32780315/could-not-find-a-part-of-the-path-bin-roslyn-csc-exe