01 - Set the oven to 400°F (200°C) and line a baking sheet with parchment paper.
02 - Heat olive oil in a skillet over medium heat. Cook diced onion until translucent for approximately 3 minutes. Add minced garlic and cook for an additional minute.
03 - Add chopped spinach to the skillet and cook until wilted, about 2 to 3 minutes. Remove from heat and allow to cool slightly.
04 - In a large mixing bowl, blend crumbled feta, softened cream cheese, grated Parmesan, egg, dried oregano, black pepper, nutmeg, and salt. Incorporate the cooled spinach mixture thoroughly.
05 - Unroll the puff pastry sheet and cut into 24 equal squares.
06 - Place a heaping teaspoon of the spinach filling onto each pastry square. Fold each over into triangles or rectangles, pressing edges firmly to seal.
07 - Place the prepared bites onto the lined baking sheet. Lightly brush tops with olive oil or a beaten egg to promote browning.
08 - Bake in the preheated oven for 15 to 20 minutes, or until puffed and golden brown.
09 - Allow the bites to cool slightly before serving.