Instructions:
- Make the Glaze: Combine balsamic vinegar and brown sugar (if using) in a small saucepan. Bring to a simmer over medium heat. Reduce heat to low and cook gently for 10–15 minutes, stirring occasionally, until the volume is reduced by about half and it is syrupy. Set aside to cool.
- Prep Marinade: In a large bowl, whisk together olive oil, minced garlic, rosemary, oregano, salt, and pepper.
- Marinate Vegetables: Toss all prepared vegetables into the marinade, ensuring everything is lightly coated. Allow to sit for at least 10 minutes while the grill heats up.
- Preheat Grill: Preheat your grill to medium-high heat (about 400°F / 200°C). Brush the grates well with oil to prevent sticking.
- Grill Hard Vegetables First: Place thicker vegetables (onions, peppers, broccoli) on the grill. Grill for 4–5 minutes per side until char marks appear and they begin to soften.
- Grill Softer Vegetables: Add the zucchini, mushrooms, and asparagus. Grill for 2–4 minutes per side until tender-crisp and charred.
- Arrange: Remove all vegetables immediately and arrange them artfully on a large platter.
- Finish: Drizzle the cooled, sticky balsamic glaze generously over the top of the platter just before serving.