**Preheat Oven:** Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
**Prepare the Filling:** In a bowl, whisk together the eggs, milk, salt, pepper, and garlic powder. Stir in the cooked sausage or vegetables and shredded cheese.
**Roll Out the Puff Pastry:** On a lightly floured surface, roll out the puff pastry sheet to a rectangle approximately 10x12 inches.
**Add Filling:** Transfer the puff pastry to the prepared baking sheet. Spread the egg mixture evenly over one half of the pastry, leaving a 1-inch border along the edges.
**Seal and Fold:** Fold the other half of the pastry over the filling to create a rectangle. Press the edges together with a fork to seal.
**Add Egg Wash:** Beat the remaining egg and brush it over the top of the pastry for a golden finish.
**Bake:** Bake for 20–25 minutes, or until the pastry is puffed and golden brown.
**Cool and Slice:** Allow the pastry to cool for a few minutes before slicing into bars. Garnish with chopped parsley, if desired, and serve warm.