Make cookie crumbs by processing chocolate cookies in a food processor until they yield a fine crumb. Add brown sugar, espresso, and oil and pulse until blended. Press mixture into the bottom and sides of a 9-inch pie pan and set aside.
Peel and thinly slice the bananas. Toss banana slices with the banana liqueur and set aside. In a large bowl, stir the marshmallow cream and whipped topping together. Fold in the banana-liqueur mixture. Spread topping over crust and smooth. Garnish with chocolate shavings, if desired. Refrigerate until chilled, at least 30 minutes.