This was part of a spy themed TOEFL class I held in the Summer for my Mexican EFL students. It would also be appropriate for ESL students of really any ELLs.
There is a worksheet which can be done as a listening task, or in pairs (in which case it is listening and speaking) and the setup for a BINGO game providing more practice. There is also a writing activity that provides a great jumping off point in the next class.
You can read more about how to teach minimal pairs here http://eslcarissa.blogspot.com/2013/09/how-not-to-teach-minimal-pairs.html