Preheat oven to 450 degrees F.
Line a large baking sheet with parchment paper.
Place the onion, zucchini, bell pepper, mushrooms, asparagus, eggplant, garlic, olive oil, salt and pepper in a large bowl and toss to combine. Arrange the vegetables on the baking sheet. Roast the vegetables 25 minutes, or until nice coloured and tender. Cool the vegetables a few minutes, and then arrange on a platter. Sprinkle with the fresh herbs and drizzle with balsamic vinegar to taste. Serve warm or at room temperature.
Note: When available, miniature zucchini and/or pattypan squash could replace the medium zucchini in this recipe.