Place 16 mini silicone muffin cases on a baking sheet.
Put the butter, syrup and sugar in a small saucepan and heat gently until the butter has melted. Stir in the oats until combined. Divide among the cases and press down gently with the back of a dampened teaspoon.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 12 minutes, or until just beginning to colour around the edges. Leave in the cases for 10 minutes, then transfer to a wire rack to cool.
Mash the banana with the lemon or lime juice until puréed. Press the purée through a sieve into a bowl, scraping off the purée that clings to the underside of the sieve. Add the cream and whisk until the mixture holds its shape.
Spoon the banana cream over the flapjacks. Drizzle with a little maple syrup just before serving.