I made this gratin a couple nights ago for dinner and it was delicious. There was just enough leftover for lunch yesterday, but I wanted to add a little something extra to up the protein. The obvious choice, a quick can of albacore tuna. The final product was a little reminiscent of tuna casserole in that it was cheesy, savory, and comforting. If I made this gratin again, Id probably just add tuna from the get-go as it makes for a more well-rounded meal.