Place the potatoes in a saucepan of water, place over a high heat and bring to the boil. Lower the heat, cover and simmer for 20 minutes or until tender.
Drain the potatoes and return to the saucepan. Add the milk and mash well. Season to taste with salt and pepper. Cover with a lid and set aside.
Spray a large frying pan with low calorie cooking spray and place over a medium heat. Add the onions and fry for 10 minutes until softened and golden brown.
Add the chicken thighs and garlic and cook for 2 - 3 minutes until sealed and lightly browned on all sides.
Lower the heat and add the cannellini beans, chopped tomatoes, tomato puree, lemon juice, BBQ seasoning, paprika, balsamic vinegar, Worcestershire sauce, white wine vinegar, hot pepper sauce, mustard powder and sweetener. Stir well then cover with a lid and simmer for 25 minutes or until the chicken is cooked and no longer pink.
Pre-heat the oven to 180ºC.
Remove the chicken thighs from the frying pan using a slotted spoon and place them on a large plate. Shred the chicken using two forks then transfer into an 18 x 27 cm ovenproof dish.
Pour the beans and sauce from the frying pan over the shredded chicken in the dish and spread out evenly.
Spread the mashed potato over the chicken mixture and swirl the top with a fork.
Sprinkle the cheese over the potato and place the dish on a baking tray.
Place in the preheated oven for about 20 minutes until golden on top and hot right through.
Serve with steamed vegetables or an accompaniment of your choice.