First, preheat the oven to 350 degrees F. Coat two 8-hole muffin pans with cooking spray. Or if you have two 12-hole muffin pans, you can use those, but only spray 16 muffin cups
Then, in a medium bowl, beat eggs, egg whites, water, salt, and pepper with a whisk until blended. Stir in spinach, artichoke hearts, feta cheese, roasted red peppers, red onion, and cream cheese, mixing well.
Next, spoon mixture into muffin cups using 1/4 measuring cup. Bake until set, about 18 to 22 minutes.
Cool in pans on a wire rack for 5 minutes. Then loosen the edges of the frittatas with a rubber spatula, sliding underneath to loosen from the bottom and lift out of the pan. Serve immediately, refrigerate in sealed containers, or freeze extras..