How do I trigger an object by pointing at it?

Hi all,

I am trying to create a 'basic; level where the player doesnt move but triggers actions in the scene by simply looking at them for a short period of time. For example, if I look at a fruit bowl for 5 seconds, it fills up with fruit, or a menu pops up. I would like this type of trigger for an android app so that no other type of interaction is needed except looking at and activating these triggers to enhance the gameplay.

Any links to tutorials for this type of scene creation would be appreciated.