Hey, it's inelegant (jam code) but the source is available here:
https://github.com/DannyT/ggj-secrets
Specifically, this is the bit which handles the interaction, I have an invisible box gameobject which I do hit detection on to determine what it's overlapping with:
https://github.com/DannyT/ggj-secrets/blob/master/src/scenes/GameScene.js#L163