What is Pam microwaving in the Frame Toby episode of season 5 The Office?

In the "Frame Toby" episode of season 5 of The Office, Pam is microwaving a piece of leftover meatloaf. She expresses her frustration with the food when she realizes that it has been in the fridge for a while. This moment adds to the humorous portrayal of the mundane aspects of office life.