Heat oven to 180°C (170°C for dark or nonstick pan). Make and bake cake as directed on box for 13x23cm pan. Cool completely, about 1 hour.
Meanwhile, in large bowl, place chopped chocolate; set aside. In 2-liter saucepan, heat whipping cream and butter over medium heat, stirring occasionally, until butter is melted and mixture comes to a boil. Pour cream mixture over chocolate; stir until smooth.
Line bottom of 23cm springform pan with waxed paper. Cut cake into 2.5cm cubes. In large bowl, beat half of the cake cubes on low speed until cake is crumbly. Add remaining cake cubes and most of the ganache (reserve some ganache for topping). Beat on low speed 30 seconds, then on medium speed until well combined (mixture will look like fudge). Fold in cut-up strawberries. Spoon mixture into springform pan; smooth top. Cover with plastic wrap; freeze about 45 minutes or until firm enough to unmold.
Run knife around side of pan to loosen cake mixture. Place serving plate upside down on pan; turn pan and plate over. Frost side and top of cake with reserved ganache. Arrange strawberry halves on top of cake.
In small microwavable bowl, microwave baking chips and 1/2 teaspoon oil uncovered on High 45 seconds, stirring every 15 seconds, until melted. Place in small resealable food-storage plastic bag; cut off tiny corner of bag. Drizzle over top of cake. Refrigerate until ready to serve. Best served the same day.