Is it appropriate to say/ask, 'So in a nutshell, how would you explain this concept?' I just sometimes feel I'm using this idiom rather awkwardly. I would like to use this idiom when I want my students to briefly explain something to check their comprehension of the topic and at the same time intentionally introducing this idiom to them. Any better sentence suggestion?
It's certainly acceptable to use it as in your example, in order to encourage the speaker to be brief. It's more polite than asking directly that they "be brief" or "answer as briefly as possible."
Another use might be after hearing an explanation or anecdote, when you might want to confirm the facts in a synopsis, beginning with the phrase, "So, in a nutshell, ..." and then recounting the salient points (briefly).
A couple of other idioms that are used for this purpose (requesting brevity) are:
- "Give me the nickel version/tour" (as in "5¢' worth", or 1/20th of a dollar's worth, and reminiscent of an accelerated tour)
- "Give it to me in bullet points" (referring to the text format of a slide presentation)
- "Give me the highlights" (referring to a recap of a sports game)
The basic meaning of this idiom is, as given by the Free Dictionary, the following:
in a nutshell In a few words; concisely
In fact they also give another example:
Just give me the facts in a nutshell.