Preheat the oven to 200C/400F/Gas 6.
For the watercress salad, place the balsamic vinegar, olive oil, salt and freshly ground black pepper into a large bowl and whisk to combine. Add the watercress and stir to coat.
For the roasted onion, heat the olive oil in a pan, add the red onion and fry over a gentle heat for five minutes until softened.
Add the sugar and cook for one minute. Add the balsamic vinegar and cook for three minutes. Set aside to cool slightly, then add to the bowl with the watercress.
For the roasted figs, place the figs cut-side up on a baking sheet and drizzle with honey. Place in the oven for five minutes, or until softened and darker in colour.
To serve, spoon the watercress salad onto a serving plate. Place the roasted figs on top and scatter with crumbled Stilton and walnuts.
