In a large bowl, mix together the mashed bananas, sugar, egg, and vanilla extract until well combined.
In a separate bowl, whisk together the flour, baking powder, salt, ground cinnamon, and ground nutmeg (if using).
Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Do not overmix.
In a deep frying pan or pot, heat vegetable oil over medium-high heat until it reaches 350°F (175°C).
Drop spoonfuls of the batter into the hot oil, being careful not to overcrowd the pan.
Fry the beignets in batches until golden brown and cooked through, about 2-3 minutes per side.
Use a slotted spoon to remove the beignets from the oil and drain on paper towels.
Dust the banana beignets with powdered sugar if desired.
Enjoy your meal!