Place 16 mini silicone muffin cases on a baking sheet.
Put the polenta, sugar, baking powder and ground almonds in a bowl. Whisk the oil with the eggs, lime juice and half the chilli. Add to the dry ingredients. Using a large, metal spoon, stir the ingredients together and stir to make a smooth paste. Divide among the cases.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for about 10 minutes until pale golden around the edges. Leave in the cases to cool.
Make the icing by using a citrus zester to pare thin curls of rind from the limes. Squeeze and measure 4 teaspoons of the juice. Beat the fondant icing sugar with the lime juice to give a consistency that thinly coats the back of the spoon, adding a dash more juice if necessary. Stir the lime rind into the icing. Place a little on each cake and spread down to the edges with a palette knife. Decorate each with one slice of chilli.