Place sausages in a medium sized baking dish & cut through the center without cutting all the way through.
Add 1 1/2 cups water to a small saucepan & heat on high with peeled diced potatoes. Boil for 10 minutes. Drain water & mash. You can add 3 Tbsp milk & 1 tsp of butter if you prefer, then mash.
Heat oil in frying pan & add onion, garlic, mushrooms & diced bacon. Gently fry until browned.
Squeeze a strip of BBQ sauce along the center of each sausage & top with a bit of cheese & the onion mix. Spoon or pipe mash potatoes on top & bake for 20 minutes.
Remove from oven & top with remaining cheese then return to oven for about 5 minutes to melt & brown. Serve.