Preheat your oven to 375°F (190°C).

In a large skillet, sauté the chopped onion and minced garlic in olive oil for 3-4 minutes.

Add the thawed and drained spinach to the skillet and cook for an additional 3-5 minutes.

In a mixing bowl, combine sautéed spinach, feta, goat cheese, cheddar, parsley, egg, nutmeg, salt, and pepper.

Brush the bottom of a baking dish with olive oil and layer two sheets of phyllo dough, brushing oil between each layer.

Spread the filling over the phyllo layers, then roll into a spiral shape.

Brush the top of the spiral with olive oil and bake for 25-30 minutes until golden brown.

Allow the spanakopita to cool for 5-10 minutes before slicing and serving.