Make the crust: Preheat the oven to 350 degrees F. Pulse the wafer cookies, sugar and salt in a food processor until finely ground. Add the melted butter and pulse until combined. Press the crumb mixture into the bottom and up the sides of a 9-inch pie plate. Bake until golden, about 15 minutes. Let cool completely.
Make the filling: Put the marshmallows, cream of coconut and butter in a saucepan and cook over medium-low heat, stirring, until smooth. Transfer to a bowl and let cool 15 to 20 minutes.
Once the marshmallow mixture has cooled, beat the heavy cream with a mixer on medium speed until stiff peaks form. Fold into the marshmallow mixture. Scatter the bananas evenly over the prepared crust, then top with the marshmallow-heavy cream mixture. Chill until the filling is firm, at least 8 hours.
To serve, beat the egg whites, marshmallow cream, sugar, lemon juice and salt with a mixer on medium speed until stiff, glossy peaks form, 5 to 8 minutes. Fold in the shredded coconut and spread over the pie with the back of a spoon. Toast the meringue with a kitchen torch or broil briefly until golden (the meringue will brown quickly).