How about letting students work in groups of 2 or 3 people to understand the next block of theory from their textbooks themselves? I am a huge believer in learning to understand mathematical notation, because this will make almost any new topic easier to learn.
I teach a supplementary statistics course and the professor supplied a set of lecture notes that students will be allowed to use during the exam. Many of them are struggling to understand the theoretical mathematical notation of the content, but for the exam they should understand what all these formulas, assumptions, etc. actually mean. Therefore, I let them help each other read little sections of the lecture notes. Basically, they're supposed to translate the formulas from mathematical notation into actual sentences. Afterwards, I give a brief explanation of what the formulas mean. I think this should work even without a lot of preparation since you know the concepts already (also, the group work phase will give you time to prepare a brief explanation).
(This probably won't work if your students are too young to even have formulas in their textbooks or if the topics are so hard that the session will end in hopeless confusion without your guidance).