Tip the couscous into a large heatproof bowl, pour over the measurement boiling water, cover and set aside for 10 minutes.
Meanwhile, put the peppers, courgettes, onions, tomatoes and garlic into a grill pan in a single layer, drizzle over the oil and cook under a preheated hot grill for 5–6 minutes, turning occasionally.
Add the asparagus to the pan and continue to grill for 2–3 minutes until the vegetables are tender and lightly charred. When they are cool enough to handle, remove the skins from the peppers and discard.
Fork through the couscous to separate the grains. Toss with the vegetables, lemon rind and juice and herbs, season to taste with salt and pepper and serve immediately with lemon wedges.