First, go to this link
and file a report with NHTSA. NHTSA will look into the report and see if yours is an isolated event or if there is a pattern. Sending a report to NHTSA is the first step in a potential recall investigation. Remember, your report may help to save somebody's life in the future.
Second, make a claim with your insurance company. Your insurance company will likely ask your local fire department for a report to make sure that this wasn't a deliberate arson case.
Third, if not already done, make sure that the fire department and/or insurance agent inspects the car and documents the findings BEFORE Subaru gets their hands on the vehicle. Why? Because you want an impartial report. Car manufacturers don't like this type of cases and you can bet that Subaru will apply a "CYA" strategy. They will blame you, the weather and the full moon before admitting that this was a vehicle fault. So make sure that the insurance and fire department can make the inspection BEFORE
Subaru tampers with the evidence.
Fourth, ask your local fire department for a report, regardless of the insurance report. You never know, it may be useful in the future, especially if your run into some issues with the insurance company (unlikely, but you never know).
Fifth, report the problem to Subaru. They will ask you to bring the vehicle to a dealer for inspection. They will probably send somebody from their tech center or plant to have a close look. By all means, take the car to the Subaru dealer, but not before the insurance and/or fire marshal inspect the vehicle. Once the car is in Subaru's hands it will be very difficult to find what really started the fire.