Prepare the crust. Mix graham crumbs, melted light butter, sweetener, and salt until the texture resembles wet sand. Press firmly into the bottom and up the sides of a 9-inch pie dish. Use a flat-bottom glass for even packing.
Set the crust. For a sturdier crust, bake at 350°F (175°C) for 8–10 minutes, then cool completely.
For a true no-bake pie, chill the pressed crust for 30 minutes until firm.
Slice the bananas. Toss sliced bananas with lemon juice to slow browning. Arrange an even layer of bananas over the cooled crust.
Whisk the filling. In a large bowl, whisk pudding mix with cold milk for 1–2 minutes until it starts to thicken. Fold in Greek yogurt, vanilla, and sweetener until smooth.
Taste and adjust sweetness.
Assemble the pie. Spread the filling over the banana layer, smoothing the top with a spatula. Tap the pie dish gently to remove air pockets.
Chill to set. Cover and refrigerate for at least 4 hours, or overnight for clean slices and a firm set.
Add the topping. Spread the whipped topping over the chilled filling. If using, garnish with fresh banana slices just before serving, plus toasted coconut or a light dusting of crumbs.
Slice and serve. Use a sharp knife cleaned between cuts for the neatest slices.
Serve cold.