Mix the salsa, mashed beans and half of the parsley in a bowl.
Season to taste with salt and pepper and set aside.
In a heavy skillet, melt the butter over medium low heat. Beat the
eggs until lemon colored, add the remaining parsley and water. Mix well and
pour into the hot skillet. Add the cheeses and cook stirring constantly
until creamy (about 5 minutes). Eggs should be set but not hard.
Spoon the egg mixture into the warm tostata shells.