Spray two baking sheets with nonstick cooking spray.
Spray nonstick cooking spray onto a clean surface and roll out pizza dough into a 15" square. Using a pizza cutter or sharp knife, cut pizza dough into 25 3-inch squares.
In a mixing bowl, combine spinach, cream cheese, 2 Tablespoons Parmesan cheese, green onion, pepper and garlic powder.
Spoon a teaspoon of spinach filling in the middle of each square and fold over into a triangle.
Use a fork to press along the edges of the triangle and seal closed.
Place mini calzones onto prepared baking sheets.
Brush egg white on the top of each mini calzone and sprinkle on remaining Parmesan cheese.
Bake for 10 minutes, or until crust is golden brown.