Mash the bananas in a mixing bowl, then add the oil, sugar, egg and vanilla to the mashed banana. Mix together thoroughly with a spoon.
Put the baking soda salt & rice flour into the mixing bowl containing your banana/oil mix. Mix all ingredients together until combined. Finally add the lemon juice and mix through.
Spoon the batter into muffin trays and put in the oven, they should take about 20 minutes to cook.