Preheat the oven to 190C/170C Fan/Gas 5. Line two baking trays with baking paper. Put the pine nuts on one and cook for 5 minutes until golden (time it, as they burn easily). Tip onto a plate.
Halve the onions, peel and cut into thin wedges. Put in a large bowl with the sweet potatoes, oil and sugar and toss to ensure they're evenly coated. Spread out on the other baking tray and roast for 15 minutes.
Add the tomatoes and cook for another 10-15 minutes, then leave to cool slightly.
Share the rocket between four plates. Add the warm roasted veg, cut the cheese into small pieces and scatter on top with the pine nuts. Drizzle on the balsamic glaze and serve.