- breakout sessions with specific tasks (a couple of students compete against other students in solving a task)
- surveys where the students have to react, e.g. with Emojis
- small sessions with fewer students (three to four) to keep them active
In my opinion, there is no need for an online session if you don't need interaction. Every simple presentation can be done via video. So I don't recommend "forcing" interaction, but rather use online sessions as a powerful tool for interaction when it is useful.
To all the recommendations already exposed, you can add the use of augmented reality through their cell phones. Maybe develop an app- or download a free one online- that allows them to interact with their environment while learning. Something similar to Pokemon Go might work. You can use this in the last 15-20 minutes of class.