Preheat oven to 350F. Microwave chocolate and oil in glass measuring cup on HIGH 1 to 2 min. or until completely melted. Stir in cocoa powder; let stand at least 5 min.
Beat egg whites and sugar in medium bowl with electric mixer on high speed 3 min. or until tripled in volume. Reduce speed to medium low; blend in melted chocolate mixture until well combined. Spoon batter into 6 paper-lined medium muffin cups. (Muffin cups can be almost full.)