Preheat the oven to 375 degrees F. Coat a 12 cup muffin pan with cooking spray.
In a large bowl, prepare muffin batter as directed.
Fold in the ham, cheese, and chives or scallions.
Spoon the batter into the prepared cups, filling each three-quarter full. Bake the muffins until their tops are lightly browned, about 20 minutes. Let them cool in the pan on a wire rack for 3 minutes, then turn them out onto the rack and let them cool completely. The muffins can be frozen in a plastic freezer bag for up to three months.