Heat olive oil in a skillet over medium heat. Add fresh spinach and cook until wilted, about 2-3 minutes. If using frozen spinach, make sure it is thawed and squeeze out excess water. Optionally, add chopped onion and sauté until softened before adding spinach.

In a mixing bowl, combine the sautéed spinach, crumbled feta cheese, minced garlic, salt, pepper, and a pinch of nutmeg. Add optional herbs such as oregano and parsley if desired. Mix well to create an even filling.

Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

On a lightly floured surface, roll out the puff pastry sheet into a rectangle shape to your desired thickness.

Spread the spinach and feta mixture evenly over half of the rolled-out pastry, leaving about a 1/2-inch border around the edges.

Fold the unfilled half of the pastry over the filling to cover it completely. Press the edges firmly to seal.

Using a sharp knife or pizza cutter, cut the folded pastry into 1-inch wide strips. Gently twist each strip to create a spiral shape.

Beat the egg in a small bowl and brush the twists with the egg wash.

Arrange the twists on the prepared baking sheet, leaving space between each. Bake for 15 to 20 minutes, or until golden brown.