Options from least to most energy- and volunteer-intensive:
Cue up a TED talk, a previous SA talk, or a talk at an adjacent organization like Oasis or Ethical Culture. Optionally discuss afterwards
Prepare video clips from an existing talk, add your own remarks and discussion questions.
Recruit a speaker from within or outside your group to present a talk.
See Finding Speakers and Themes and Speaker's Guidelines on page 20 of the Start-Up Guide.