Preheat oven to 350°F.

Spray a 12-cavity muffin tin generously with nonstick cooking spray.

Finely chop the scallion and set aside. Finely dice the vegetables and place in a large skillet.

Set the skillet over medium-high heat, and pour in the water. Cook the vegetables, stirring frequently, until the water is completely evaporated and the vegetables are softened. Transfer to a large mixing bowl.

Pour the liquid egg whites into the mixing bowl. Add the scallion, salt and black pepper. Fold with a rubber spatula to distribute the vegetables.

Divide the mixture evenly between the 12 cavities of the muffin pan.

Bake the egg muffins on the middle rack of oven until golden brown on top and a toothpick inserted in the center comes out clean, 20-25 minutes.

Check to see that muffins are done. Remove from oven or add time as needed.

Allow the muffins to cool for 5 minutes in the pan. To remove, run a sharp knife around the edge of each muffin and lift up at an angle. Plate and serve.