Pre-heat the oven to 170°C.
Place the potatoes in a saucepan of cold water and the swede into a second saucepan of cold water.
Place both saucepans over a high heat and bring to the boil. Reduce the heat to a medium setting and partially cover each with a lid. Simmer the potatoes for 20 minutes and the swede for 30 minutes, until tender when tested with a knife.
Drain the potatoes and return to the saucepan. Drain the swede and return to the other saucepan.
Add half of the reduced fat spread and half of the milk to the potatoes and mash well. Season well with salt and pepper. Cover with a lid and set aside.
Add the remaining reduced fat spread and milk to the swede and mash well. Season well with salt and pepper. Cover with a lid and set aside.
Spray a frying pan with low calorie cooking spray and place over a low heat. Add the onion and fry for 15 minutes, stirring occasionally, until softened and golden brown. Add the garlic for the last 3 - 4 minutes of cooking. Set aside.
Use a food processor, stick blender or grater to turn the bread into breadcrumbs, and place in a small bowl.
Add the cheese, dried onion granules and parsley to the bowl of breadcrumbs. Season well with salt and pepper and stir to combine.
Place the mashed potato in the ovenproof dish and spread out evenly.
Spread the onions over the potato, and then place the mashed swede on top and spread out evenly.
Sprinkle the breadcrumb mixture over the swede and place on a baking tray.
Place in the preheated oven for 20 - 25 minutes until golden brown on top and hot right through. Serve.