Cook the potatoes on a bed of sea salt for 40-45 minutes.
For the topping, heat olive oil in a shallow nonstick pan. Add the red, yellow and green bell peppers to the pan. Add mushrooms, salt, crushed black peppercorns and red chilli flakes. Toss quickly.
Add the sausages, toss once more. Remove from heat and set aside.
Once the potatoes are cooked, transfer them onto a cutting board and cut it lengthwise into half.
Onto a serving plate, place the potatoes and sprinkle a pinch of salt. Top it with the sausage mixture, sprinkle spring onions and cheese.
Top up with mayonnaise and ketchup. Sprinkle the chopped parsley and serve immediately.