Preheat the oven to 325°F. Line a jelly roll pan or a 15x10-inch baking sheet with parchment paper and spray with vegetable spray - spray underneath it too so it doesn't move.
In a small bowl whisk the flour, salt, and baking soda together.
In a separate medium-sized bowl beat the egg whites until frothy.
Add the sugar, cocoa powder, oil, and vanilla to the egg whites and beat on medium speed until smooth and combined.
Add the flour mixture and beat on low until combined. Stir in the chocolate chips.
Scrape the batter onto the pan and spread from edge to edge with a rubber spatula or frosting spatula - the batter will be thin.
Bake 25 minutes. Cool in pan on wire rack.