Saute spinach, onions, salt, pepper and cinnamon in olive oil for 3-5 minutes, until onions are translucent. Set aside to cool.
In a large bowl, combine cheeses and eggs. Add cooled spinach mixture and stir well.
Layer 6-8 sheets of phyllo dough in a 10x15 pan, brushing melted butter between layers.
Spread ½ of the spinach mixture over dough.
Repeat with 6-8 more sheets of dough, brushing melted butter between layers.
Then spread the rest of the spinach mixture over dough and 6-8 more sheets of dough, brushed with butter.
Bake in a 350 degree oven for 45 minutes or until golden.