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.