1. In large skillet over medium heat, heat oil and cook onions until tender and golden. Add spinach and heat through. Remove skillet from heat.
2. To onion & spinach mixture, add cottage/ricotta cheese, cream cheese, feta cheese, Greek seasoning, and egg. Mix well.
3. Remove half of the phyllo sheets from package; keep remaining phyllo wrapped with plastic wrap to prevent drying out. Brush bottom and sides of 13x9" baking pan with some of the melted butter. Working quickly, place 2 sheets of phyllo in baking dish, pressing phyllo against side of dish. Lightly brush with butter. Repeat layering and brushing until first half of phyllo sheets are in the pan.
4. Spread the spinach mixture evenly over phyllo in baking dish.
5. Unwrap the remaining phyllo and layer with butter over spinach mixture, letting edges hang over sides of dish; brush edges with butter, making sure to moisten. When layering is complete, tuck edges into pan.
6. Bake in pre-heated 350 degree oven for approximately 45 minutes (adjust time accordingly for your oven). Cut into squares and serve.