Preheat oven to 350°F. Coat two 8-hole muffin pans with cooking spray (or use one 12-hole pan and four holes from another muffin pan).
In a medium bowl, beat eggs, egg whites, water, salt and pepper until blended. Stir in spinach, artichoke hearts, feta, roasted peppers, scallions and cream cheese; mix well.
Spoon about 1/4-cup egg mixture into each prepared muffin hole. Bake until just set, about 18 to 22 minutes. Cool in pans on a wire rack for 5 minutes. Loosen edges of frittatas with a rubber spatula, sliding spatula underneath frittatas to loosen bottoms and lift frittatas out of pans; serve. Yields 1 frittata per serving.