For filling: In a large skillet melt butter over medium. Add onion and garlic. Cook and stir 5 minutes or until onion is tender. In a medium bowl combine onion mixture, spinach, feta, and oregano.Advertisement
Line a large baking sheet with waxed paper. Unfold phyllo; remove a sheet. (Keep remaining phyllo covered with plastic wrap to prevent it from drying out.) Lightly brush sheet with some of the melted butter. Place another phyllo sheet on top; brush with butter.
Cut the two layered sheets lengthwise into three strips. Spoon one rounded teaspoon filling 1 inch from one end of each strip. To fold into a triangle, bring a corner over filling so short edge lines up with a long side edge. Continue folding the length of strip to form a triangle that encloses the filling. Place on prepared baking sheet. Repeat with remaining phyllo, melted butter, and filling. Freeze 1 hour or until firm. Transfer to freezer containers. Freeze up to 2 months.
To serve: Preheat oven to 375°F. Place frozen triangles on a baking sheet; brush with additional melted butter. Bake 15 minutes or until golden. Serve warm. Makes 36 spanakopita.