Preheat the oven to 350°F (176°C) and prepare an 8×8-inch baking dish with parchment paper or grease a standard pie dish.
Blend oats, almonds, salt, and sugar in a high-speed blender until a fine meal forms.
Add melted coconut oil and pulse until a dough forms.
Adjust the oil if the mixture is too dry.
Press the dough evenly into the prepared pan using parchment paper and a flat-bottomed object.
Bake for 15 minutes at 350°F, then increase to 375°F (190°C) and bake for another 5–10 minutes until golden brown and let cool.
Combine cornstarch, sugar, salt, and almond milk in a saucepan, whisking to avoid clumps.
Heat the mixture over medium heat until it bubbles, then reduce to low and cook for 4–6 minutes while stirring constantly.
Remove the pudding from heat when it thickens, stir in vanilla, and cool for 10 minutes.
Transfer to a bowl, cover with plastic wrap touching the surface, and refrigerate for 2–3 hours.
Chill a mixing bowl in the freezer, then scoop hardened coconut cream from a refrigerated can into the bowl.
Beat the coconut cream with a mixer until whipped, adding vanilla and powdered sugar, and refrigerate for at least 30 minutes.
Combine the cooled pudding and whipped coconut cream gently until just mixed, then refrigerate.
Layer sliced bananas on the cooled crust, add the custard mixture.
Smooth the top, and refrigerate for at least 4 hours or overnight to set.