you can bypass the awkwardness by preparing your response in advance.
Frame your explanation around what the hiring manager likely wants to know:
Reason for the firing – was it for something serious like stealing or a lesser infraction like not meeting your sales goals?
That you take responsibility for your actions and have grown from the experience. Bonus points if can give an example of the steps you have taken to grow/improve
Reassurance that the issue is no longer a problem
Follow these additional #tips:
Provide a direct and upfront response; make it short and to the point - Briefly explain the reason; be honest and keep it simple
Gently move the conversation forward - Reiterate your interest in the job and promote your relevant skills and experience
Be professional and positive; do not pass blame or talk negatively about former employers
Practice your response until you feel comfortable