Preheat the oven to 180°C, and grease an 18 x 27cm ovenproof dish with a little low-calorie cooking spray.
Place the potato halves on a chopping board, flat-side down.Make narrow, evenly-spaced cuts across the width of each potato half, working from one end of the potato to the other end. Cut as far into the potato halves as you can, but don't cut right through.
Place the potato halves flat-side down in the greased ovenproof dish.
In a heatproof jug, mix the boiling water and stock cube until dissolved, then add the cream cheese, garlic, and season well with freshly-ground black pepper. Stir until the cream cheese has completely dissolved, and the mixture is smooth.
Pour the cream and stock mixture over the potatoes in the dish. They should be almost submerged, with just a little of their tops visible.
Sprinkle over half of the Cheddar, half of the bacon and two of the sliced spring onions. Place in the preheated oven, uncovered, for 40 minutes – until the potatoes are just tender.
Remove from the oven and sprinkle with the remaining Cheddar and bacon. Return to the oven and continue to cook, uncovered, for a further 30 minutes, until the potatoes are soft inside and the top is bubbling and golden.
Sprinkle the top with the remaining sliced spring onion, and serve alongside other sides and a main dish of your choice.