A great initiative from The Chapel. They have a ‘hard questions’ section on the homepage of their website. It looks like this:

This would tie in well with a community letterbox drop - invite locals to visit the your church’s website and ask their tricky questions. You could then let people know that in month X later in the year, the top 5 topics, as voted by them, would be preached on in the church.

This reminds me of Mars Hill’s ‘Ask Anything’ series back in 2007, although it was aimed (from what I can gather) more at Christians: