Lightly grease an 18 cm/7 in square shallow cake tin.
Roughly chop the dates and bananas.
Place them in a heavy based saucepan, together with the lemon juice, honey and water.
Simmer the mixture gently over a low heat for about 30 minutes, or until softened.
Leave it on one side to cool.
Meanwhile, make the base and topping.
Place the sugar, butter and oats in a large, heavy based saucepan.
Heat these ingredients gently, stirring occasionally, until the sugar has dissolved and the butter has melted.
Increase the temperature slightly and continue to cook, stirring continuously, until the sugar caramelises and the oats turn a light golden brown.
Spoon half the mixture into the prepared tin and level the surface with the back of an oiled metal spoon.
Spoon the date filling over the base, then top with the remaining oat mixture.
Press down lightly with the spoon and mark the date and banana biscuit into squares while still warm.
Leave to cool completely before cutting the biscuit into squares.