Preheat oven to 375F. Butter a 8 inch spring form pan and set aside.
In a small saucepan, heat oil over medium heat. Sauté the onions until translucent and tender about 2-3 minutes. Set aside
In a large bowl, add the spinach, parsley, green onions, cooked onions, feta, halloumi and beaten eggs. Season with salt and pepper and toss gently until well mixed. Set aside.
Combine the melted butter with the olive oil in a bowl.
Place phyllo between a damp tea towel, this will ensure it does not dry out.
Using a pastry brush, brush 8 sheets of phyllo with butter mixture. Layer them in pan with edges of phyllo are draping over sides of pan
Fill with spinach mixture and fold edges over.
Layer 8 more sheets of phyllo, brushing each with melted butter. Ensure the sides of the phyllo are tucked in the spring form pan.
Bake for 45-50 minutes or until pie is dark golden in colour. Remove from oven, allow to cool for 5 minutes prior to removing from spring form pan.