The tenant is behind on their gas utility payment, and I know this is not considered rent as per the Act. I do not see a form available that applies to this situation, what can I do to recover this money?

If the tenant is still in possession of the rental unit a landlord can file an L2 application for failure to pay utility costs with the LTB, to recover the costs for the utilities. You can also serve the tenant with and N5 Notice. The notice gives the tenant 7 days to pay the utilities and if the problem is not corrected within a specified time period (7 days) then you could file an L2 application to the Landlord and Tenant Board seeking an order to terminate the tenancy and recover the unpaid utility costs from the tenant. If the tenant has already moved out, you can file an L10 application with the LTB to recover unpaid utility costs for up to one year after they leave the unit. The prescribed forms are available at http://tribunalsontario.ca/ltb/forms/.