While the cupcakes are cooling melt the chocolate chips in the microwave for 30 seconds and stir. Continue heating in 10-second increments, stirring after each one, until completely melted. Pour chocolate into a disposable piping bag fitted with a Wilton #1 round tip.
On a sheet of wax or parchment paper pipe the handles for your lawn mowers by making a rounded rectangle about 1 1/2" high with a crossbar. Make more than you think you need in case some of them break. Put in the freezer for 15 minutes until solid.
While the handles set unwrap the Hershey's Nuggets and attach the M&M wheels using the melted chocolate. Freeze for 15 minutes.
Once the body and handles of the mowers have set remove them from the freezer and attach the handles to the body of the mower with melted chocolate. Do this quickly because the chocolate will harden fast on the frozen pieces!
Put the assembled lawn mowers back in the freezer for another 5 minutes.