Easiest way to connect the the DB ..or to a plugin from a Controller

What is the easiest way to connect from the CheckOut Controller ...to the DBContext so that I can run a quick Stored Proc?
I could also run it from a plugin, doens't really matter.

I just need to know how to connect to either a DBContext or a PlugIn.

Any help is truly appreciated.

Just for future references, I had to extend an existing Service and pass the service the Controller directly.