Place a 9-inch springform pan in the freezer to chill while preparing the next steps.
Cut each ice cream sandwich into quarters (slicing in half lengthwise, then in half crosswise). You will end up with a total of 32 pieces. Transfer the pieces to a wax-paper lined pan, and freeze until firm again. Meanwhile, remove strawberry ice cream from freezer and allow to soften for next step.
Remove the springform pan and the ice cream sandwiches from the freezer. Line the outer rim of the springform pan with the ice cream sandwiches, arranging them lengthwise. Working quickly, fill the center of the pan with the softened strawberry ice cream. Cover and freeze until very firm, at least 2 hours. This part of the cake can be prepared and frozen for up to 1 week.
Warm the hot fudge for 20 to 40 seconds in the microwave, then stir to evenly heat. Remove the cake from the pan and transfer to a serving plate. Pour the fudge sauce on the top center of the cake and spread just to the edge of the strawberry ice cream filling. Dollop with the whipped cream, then layer the banana slices around the edge. Garnish with chopped walnuts and top with a cherry. Serve immediately.
Source: America's Test Kitchen, Best Summer Desserts