Preheat oven to 450°F.  

Coat ten cups of a popover pan or ten 2 1/2-inch muffin cups with cooking spray or softened butter. Fill any empty cups with 1/2-inch of water so the pan does not burn.

In a large bowl, whisk together the flour and salt. In a second bowl, whisk together the eggs and milk. Add the egg mixture to the flour mixture and stir just until mixed. Stir in the shredded cheese and chopped green onions. Fill the prepared cups about three-quarters full with about 1/3 cup of the batter. 

Bake for 15 minutes. Reduce the oven temperature to 350°F. Bake an additional 10 to 15 minutes or until browned and puffed.  Do not open oven door until the end of baking time or popovers will collapse. 

Remove from the oven and immediately remove the popovers from the pans. Pierce the side of each popover with a knife to release steam.  Serve immediately while still warm. 

If necessary, reheat popovers in a 350°F oven for 5 minutes to crisp outside edges.