Mix the eggs and 1 tablespoon water into a large bowl. Spray a large round skillet with cooking spray. When the pan is hot enough that water dances on the surface when sprinkled, it is ready.
Pour half the egg mixture into the pan. Tip the pan around so it fills the entire pan, and cooks the whole egg. Push the egg towards the center, and let the uncooked egg fill the pan again. Do this until the eggs are almost set.
When it's almost cooked, sprinkle 1/4 cup black beans, and 2 ounces of shredded mozzarella onto half the omelet. Fold the other half of the omelet over it, and continue to cook until the cheese is melted.
Repeat this for the rest of the eggs and you will have two large omelets that should be cut in half for four servings.
Top with prepared salsa, and serve with diced mango.