Pre-slice all the vegetables because once they go on over flame, they will cook quickly. Toss the vegetables in the olive oil, salt and pepper in a large sheet tray or bowl.
Preheat the grill using the gradient method and lump charcoal. Target the temperature on the hottest side at 550 degrees Fahrenheit while the side with less charcoal is around 375 - 400 degrees F.
Over the highest heat place the onions, peppers, and squash. Grill for a few minutes per side until you see grill marks and then finish them on the cooler side.
Over the middle of the grate and heat, add the broccoli, asparagus, and similar sized items.
Leave the cooler side to move veggies to as they need to finish and so they don't burn.
Remove the veggies as they finish. Scrape charred skin off the peppers and serve on a large serving platter with tongs.
Drizzle a light coating of aged balsamic and a sprinkle of finishing salt. These are great served hot or cold.
Notes
Optional - For the mushrooms marinade, remove gills from mushroom cap and the stem. Marinade for 2 hours prior to grilling.