Preheat oven to 425°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 5 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.