Split muffins in half horizontally and arrange in a single layer, cut sides up, on a 14- by 17-inch baking sheet. Lay bacon slices in a single layer in a 10- by 15-inch pan.
In a 450° oven, bake muffins and bacon until browned, 5 to 7 minutes.
Place 2 muffin halves, cut sides up, on each plate. Lay 1 bacon slice on each muffin half; set 1 egg on each slice of bacon. Spoon hollandaise equally over portions. Arrange watercress next to muffins.