Preheat oven to 400°F (200°C). Slice baguette into 36 rounds. Arrange, in a single layer, on a baking sheet lined with parchment.
Spread some mustard on one side of half the slices. Top with a piece of ham and cheese; cap with remaining baguette slices. Stir yogurt with Parmesan, green onion, melted butter and nutmeg. Dollop over each sandwich. Top with remaining piece of cheese.
Bake for 5 minutes or until cheese is melted. Set the broiler to high. Broil for 5 to 7 minutes or until tops are bubbling and lightly browned.
These mini sandwiches are also great with roasted turkey and Cheddar cheese.