Preheat the oven to 180°C.
Cut the squash in half (lengthwise) and remove the seeds. Brush them with olive oil, then put them onto a baking sheet, facing upwards.
Bake the squash until tender (it should take about 30-45 minutes).
Cut the bacon into small cubes and fry them a frying pan, until golden and crispy. Add the walnut pieces, stir for 30 seconds and pour in the vinegar. Let it sizzle for few seconds, then remove from the stove.
Using a fork, loosen the flesh of the baked squash, then top with the bacon & walnut mixture. Season with freshly ground pepper.
Serve warm.