Grease a 20cm square tin lightly. Preheat the oven to 180°C (gas 4) and 160°C (fan). In a large mixing bowl, toss the apples with the cinnamon and sugar, then lay out on a baking sheet and roast for 10 minutes. Remove the baking sheet from the oven and set it aside.
In a food processor, combine the oats, prunes, raisins, peanut butter, and honey and pulse a few times to combine and mash the ingredients.
Roughly spoon the mixture into the prepared cake tin, then top with the roasted apple and press into the mixture.
Bake for 15 minutes in a preheated oven. Remove the pan from the oven and cool for 15 minutes before cutting into 9 squares to serve.