Place the bread in a food processor and pulse to form fine bread crumbs. Season generously, add the toasted walnuts, and pulse again to combine. Set aside until needed.
Heat 1 tablespoon of the olive oil in a large pan over medium heat. Add the celery, shallots, and garlic to the pan, season, and sweat for 4 to 5 minutes until translucent.
Add the parsnip, carrot, and oregano to the pan, season generously, and sauté for 5 minutes until softened. Reduce the heat to low, add the whole-grain mustard, margarine, remaining olive oil, and the bread crumb mixture and stir well to combine, then remove the pan from the heat and stir through the chopped figs and parsley.
Spoon the stuffing mixture into a lightly greased 1 lb loaf pan a little at a time, pressing down firmly with the back of a spoon to compact it nicely. Cover with aluminum foil and refrigerate overnight (you can cook it straight away but this chilling will result in a firmer slice).
When ready to cook, preheat the oven to 425°F.
Bake covered for 45 minutes, then remove the foil and bake for another 10 to 15 minutes until nicely browned. Remove from the oven and let cool in the pan for at least 10 minutes before gently tipping it out onto a serving plate. Cut into slices and serve.