1. Finely chop the prunes and place them in a small saucepan with the water. Bring to the boil, then remove from heat. Puree using a blender or mash well with a whisk until smooth.
2. Add the margarine, brown sugar, cinnamon and half of the raisins, stirring well until combined. Return the saucepan to low heat and gently simmer for 5 minutes, stirring frequently so it doesn't burn. Remove from the heat.
3. Into a large bowl add the oats, seeds, coconut and remaining raisins and mix well. Create a well in the centre.
4. Pour the warm prune mixture into the well and mix well until all ingredients are combined.
5. Line the air fryer basket with baking paper, allowing a 2–2.5 cm overhang around the edges. Lightly spray the paper with oil. Press the mixture firmly and evenly onto the paper, using the back of a large metal spoon to compact it well.
6. Cook at 140 °C for approximately 30 minutes, checking at 20 minutes as appliances may vary.
7. Carefully lift the slice out of the air fryer and allow it to cool to room temperature. Transfer to the refrigerator to fully set before slicing.