Put the peppers, courgettes, mushrooms and aubergine in a large mixing bowl. Add 3 tbsp oil and the dried mixed herbs, then season with freshly ground black pepper and mix until well combined.
Put the vegetables on a preheated barbecue or griddle pan and cook for 5-7 minutes, turning once. Just before the end of the cooking time, brush the cut side of the ciabatta rolls with the remaining oil and grill cut-side down until lightly golden.
Put the ciabatta rolls on a serving platter alongside the grilled vegetables, salad leaves and sour cream and chive dip, then let everyone build their own burger.