1) Place a griddle pan over medium-high heat or prepare the barbecue to medium-high heat. Brush the vegetables with 60ml of the oil to coat lightly. Sprinkle the vegetables with salt and pepper.
2) Working in batches, griddle the vegetables until tender and lightly charred all over, about 8 to 10 minutes for the peppers, 7 minutes for the yellow squash, courgette, aubergine, and mushrooms, 4 minutes for the asparagus and spring onions. Arrange the vegetables on a platter. The key to getting those great grill marks is to not shift the vegetables too frequently once they've been placed on the hot griddle.
3) Meanwhile, whisk the remaining 2 tbsp of oil, balsamic vinegar, garlic, parsley, basil, and rosemary in a small bowl to blend. Add salt and pepper to taste. Drizzle the herb mixture over the vegetables. Serve the vegetables, warm or at room temperature.