Line a 6-inch round glass storage dish with plastic wrap. I use a 3-inch deep Pyrex container but you can also use a springform pan.
Prepare crust by pulsing oats in blender until powered. Add dates, coconut oil and salt and blend until crumbly, sticky dough is made. Use your fingers to spread and press dough evenly onto the bottom of the dish.
Blend fresh and frozen bananas together until smooth. If using a low power blender you made need to add a tablespoon or two of nondairy milk to get things going.
Pour 3/4 of banana mixture over crust layer in dish.
Blend remaining bananas mixture with cacao powder. Pour over plain banana layer.
Cover and place in freezer until completely frozen (4-6 hours).
Let cake defrost for 5 minutes, then gently pull plastic up to pop cake out of glass dish.