Spoon vanilla ice cream into the cookie crust; spread evenly. Place in freezer about 15 minutes until just firm.
Spoon fudge sauce into a ziptop freezer bag, snip one corner and pipe sauce in an even layer over ice cream. Top with bananas. Freeze about 30 minutes until just firm.
Spoon chocolate chocolate-chip ice cream over bananas, spreading as evenly as possible. If needed, place in freezer to firm. Scoop dulce de leche ice cream on top. Spoon dollops of whipped topping around top edge of pie. Freeze until firm; top slices with more dollops of whipped topping, and walnuts if using.