Make-Ahead Egg and Cheese Sandwich

In a bowl, beat eggs with 1 Tbsp water and ¼ tsp each salt and pepper. Heat oil in a large non stick skillet on medium heat. Add eggs and cook, stirring with a rubber spatula every few seconds, to desired doneness — 2 to 3 minutes for medium soft eggs. Spoon onto bottom half of each muffin and top with cheese, spinach, and ham (if using). Sandwich with remaining muffin top.