Sift the flour, baking powder, bicarbonate of soda and salt into a big bowl. In a separate bowl, mix together the bananas, sugar, egg, milk and oil.
Now add the wet ingredients to the dry and stir until they come together to form a batter. No flour should be visible, but the mixture should still be lumpy so be careful not to overmix. Add the nuts, if using, and pumpkin seeds, and stir them in.
Spoon the batter into paper cases set in a muffin tray. Sprinkle the extra pumpkin seeds over the tops of the muffins, then bake for 20–25 minutes until the tops are lightly browned and springy to the touch. Cool on a wire rack.