Preheat the oven to 200°C/fan oven 180°C/gas mark 6.
Put the vegetables on to a baking sheet and sprinkle with the oil. Add the rosemary and season with black pepper. Roast for 20-25 minutes, until the vegetables are tender.
Roast the vegetables in advance, then cool them. Keep them in a covered dish in the fridge for up to 3 days, ready to use for the sandwiches.
To make the sandwiches, spread each slice of bread with hummus, then top 4 slices with the chicken. Share the cooled vegetables between them and add some salad leaves. Top with the remaining slices of bread, cut in half and serve.
For a vegetarian version, have a little reduced-fat grated cheese instead of chicken, or simply use some extra hummus.