Preheat oven to 425 degrees F. Coat 12 (2 1/2-inch) muffin tins with nonstick cooking spray. Place 4 potato nuggets in each muffin tin. Bake for 12 minutes. Remove from oven. Use the bottom of a 1/4-cup measure to press the potatoes into the bottom and part way up the sides. Return to the oven and bake 12 minutes more.
Divide ham among cups. Bake for 10 minutes more or until cups are crisp and brown and ham is heated through. Remove from oven.
Divide cheese among cups. Bake 5 minutes or until cheese is melted and edges are golden. Remove from tins. Garnish with green onions or chives.