Preheat the oven to 350°F (180°C). Mash peeled bananas in a large bowl with a fork until mostly smooth, leaving some small chunks. Stir in melted butter, olive oil, applesauce, spices, sugar, and vanilla until fully combined, then mix in one egg.
Add flour, baking powder, salt, and baking soda to the wet ingredients and gently stir until combined.
Line a muffin tin with liners and spoon the mixture into each, filling about 3/4 full to yield 11-12 muffins. Sprinkle a small pinch of oats on top if desired.
Bake for 15-17 minutes until light brown and set. Remove from the oven while slightly underdone to maintain moisture, and allow the muffins to cool in the pan for at least 5 minutes before removing and serving.