Preheat the oven to 190 degrees C. Lightly coat a 12-hole muffin tray with cooking spray. Combine 1/3 cup (50g) of the flour, 1/3 cup (50g) of the brown sugar, 1 sachet of the porridge and the margarine in a small bowl. Rub in with your fingertips until the mixture is crumbly. Set aside until needed.
Mix the remaining flour and porridge mix with the bicarb soda and mixed spice in a medium bowl, and make a well in the centre.
Stir together the apple sauce, oil, remaining brown sugar and the eggs in another bowl until the brown sugar has dissolved. Pour into the well in the dry ingredients and stir until just combined (do not overmix; the mixture should be lumpy). Stir in the apple.
Spoon the mixture into the muffin tray. Sprinkle with the crumble topping. Bake for about 20 minutes or until a skewer inserted in the centre of a muffin comes out clean. Cool the muffins on a wire rack.