Hooray for making it up as you go along!
Cut a couple chicken breasts mostly through so that they can be stuffed. Smear the insides with good mustard, then add smoked ham and gruyere. Fasten with toothpicks. Cook in a hot pan so that both sides brown nicely, serve when the cheese starts to flow.
We ate this with rice and raddicchio that I sauteed with leeks, diced carrots, and a bit of wine vinegar at the end.