Prepare the crust: In a food processor, pulse oats, almonds, coconut sugar, and salt to a coarse meal.
Drizzle in melted coconut oil and pulse. Add water 1 tablespoon at a time until the mixture holds when pressed. Press firmly into a 9-inch pie dish, going up the sides.
Bake and cool: Bake the crust at 350°F (175°C) for 10–12 minutes, until lightly golden and set.
Cool completely on a rack. A cooled crust prevents sogginess later.
Whisk the custard base: In a saucepan off heat, whisk milk, maple syrup, cornstarch, egg yolks, vanilla, and salt until smooth with no lumps. This prevents streaky custard.
Cook to thicken: Set over medium heat and cook, whisking steadily, until it bubbles and thickens to a pudding-like consistency, 5–8 minutes.
Remove from heat.
Add the banana and yogurt: Whisk in the mashed banana until blended. Let the mixture cool 5 minutes, then fold in Greek yogurt until silky. Taste and adjust sweetness if needed.
Layer bananas: Slice 1–2 bananas.
If you’re worried about browning, lightly brush slices with lemon juice. Arrange a snug single layer over the cooled crust.
Fill the pie: Pour the warm banana-yogurt custard over the banana layer. Smooth the top with a spatula.
Chill to set: Cover and refrigerate for at least 4 hours, ideally overnight.
The pie firms up and slices cleanly when fully chilled.
Add the topping: Just before serving, spread a thin layer of light whipped topping or whipped coconut cream. Keep it airy; you don’t need much.
Garnish and serve: Add shaved dark chocolate, toasted coconut, or crushed nuts if you like. Slice with a sharp knife, wiping between cuts for neat slices.