Pan-fry Beef and Broccoli according to package directions. Let cool to room temperature.
In small bowl, whisk egg with 1 tbsp water.
Lightly dust work surface with flour. Arrange pastry sheets on top and cut each into four 5-inch squares (for 8 squares total).
Spoon 2 tbsp Cheddar into center of each pastry square. Top evenly with beef and broccoli. Brush edges of pastry lightly with egg wash. Fold each pastry square diagonally to create triangle pockets. Press pastry edges together and seal with tines of fork. Transfer to parchment paper–lined baking sheet. Brush with egg wash. Cut small vent hole in center of each hand pie.
Bake for 20 to 25 minutes or until golden brown. Serve with chimichurri sauce.
Tip: Alternatively, serve with salsa if preferred.