To make the filling, finely chop 1/2 small onion (about 1/3 cup chopped onion).
Saute in olive oil until transparent.
Squeeze water out of thawed chopped spinach.
Add to onion and saute until all water is gone. Allow to cool.
In large bowl, mix ricotta with one egg. Stir in onion and spinach mixture.
Add 1/2 cup parmesan or mozzarella and mix well.