Preheat the grill. Toss the mushrooms, red and green peppers, onion and chillies with the olive oil and season generously with salt and pepper. Spread out the vegetables on to a large nonstick baking sheet and cook under the grill for 4–5 minutes each side until charred and almost tender, then tip on to a chopping board.
When the vegetables are cool enough to handle, chop into bite-sized pieces and set aside to cool.
To make the harissa dressing, mix all the dressing ingredients in a small bowl until well combined and set aside.
Put the chopped vegetables, tomatoes, drained chickpeas and dressing in a large bowl and toss until well combined. Spoon the salad on to serving plates and top with the chopped egg and black olives.