Not really a mousseline, because the overcooked meat will effect the texture. However, a great way to salvage over cooked meat is as a filling; ravioli, wonton, egg roll, cannelloni, etc. You can then take it to the next level with a little bit of creativity to dress it up some. For example, I would grind it up with caramelized onions, blanched spinach and some other goodies, and then roll it up in a potato sheet and pan fry. Then you would end up with a Potato Beef “Cannelloni” that would utilize your waste product and offer value in your customer’s eyes.