PREHEAT oven to 350° F. Line 9-inch-square baking pan with foil.
COMBINE flour, cocoa, baking soda and salt in medium bowl.
MELT ¾ cup morsels in large, microwave-safe bowl on HIGH (100%) power for 1 minute; stir until smooth. Cool slightly. Stir in oil, brown sugar, granulated sugar, egg whites and vanilla extract. Stir in flour mixture; fold in zucchini. Spread into prepared pan. Sprinkle remaining ¼ cup morsels over top.
BAKE for 30 minutes or until wooden pick inserted in center comes out slightly sticky. Cool completely in pan on wire rack. Lift brownies from pan; cut into 16 squares. Store in airtight container for up to 5 days.