According to my game book, that was totally an Approach Invitation. As you know, I am mainly a day gamer and i am always alert to those types of events. Is as if they are giving you the opener in a silver plate. You just have to ask them or comment about it. They are giving you the sign. I would just have gone and said: A banana (tone is important but really almost any tone does either question, exclamation mark, complicity… what ever comes natural). She will have to fill in with some comment and you have the conversation rolling.
Anyhow, the following is a great thread I found really useful: