Preheat the oven to 180°C fan / 400°F and line the base and sides of an 8” x 8” baking tin with baking paper.
Add the banana, oats, sunflower seeds, pumpkin seeds, raisins and walnuts and a pinch of salt to a mixing bowl.
Then transfer the peanut butter, maple syrup and coconut oil to a small pan on a low heat. Stir to combine and leave on the heat until melted.
Pour the peanut butter liquid and milk into the mixing bowl and stir until the dry ingredients are fully coated with the wet ingredients.
Transfer the flapjack mix to the pre-lined baking tin and use a spatula to level the mixture. Bake for 30 minutes.
Remove the flapjack from the oven and leave to cool in the tin for 5 minutes. This will set the flapjack so it doesn't break when you move it.
Remove the flapjack from the tin and leave to cool for 10 minutes before cutting into 10 bars.