Preheat oven to 180ºC. Grease 20 x 30cm rectangular cake pan with butter; sprinkle lightly with flour. Line bottom with baking parchment paper.
Beat the cake mix, oil, water and eggs in a large bowl with electric mixer on low speed until moistened. Beat on medium speed for 2 minutes. Fold in the orange zest. Pour into pan.
Bake 40 to 45 minutes or until toothpick inserted in center of cake comes out clean. Cool 10 minutes. Remove cake from pan to cooling rack.
Heat honey and 3 tablespoons water in small saucepan over low heat. Cook 2 minutes; stir in the orange blossom water and ground cardamom. Remove from the heat. Pierce the cake all over with a fork or toothpick. Slowly pour honey mixture over top of warm cake, allowing it to soak into the cake. Cool completely.
Meanwhile, combine sugar and 300ml water in a medium saucepan. Cook over low heat until sugar is dissolved, stirring occasionally. Increase heat to medium high; bring mixture to a boil. Add orange slices; reduce heat to low. Cook 30 minutes or until orange slices are tender.
Place wire cooling rack over shallow baking pan. Remove orange slices to wire rack; cool completely. Return sugar mixture to heat; simmer 5 to 8 minutes or until mixture has reduced and thickened.
Beat whipping cream mix and cold milk in medium bowl as directed on package.
Decorate the cake with the orange slices and drizzle over the reduced candied orange syrup. Serve with the whipped cream.