First prep the vegetables. Make sure they're clean and dried off, if necessary. Particularly for the mushrooms you'll likely need to wipe off any dirt and grime with a paper towel. Take out one or two large rectangular dishes or a plastic ziploc bag to put the prepped veggies into for marinating.

Starting with the asparagus, take the stiff, woody ends off of them. You can either bend them until they snap off, or cut the off with a sharp knife on the cutting board. Set them in the dish when done.

For the onion, peel the papery outside layers off, then cut it into roughly half inch slices with a sharp knife on a cutting board. Slide a toothpick into each slice until it reaches the middle to help keep the onion layers together, then place the onion slices in a dish as well.

To prep the bell pepper first you'll need to remove the tops. Make an incision less than half an inch down from the top of the pepper and carefully cut all the way around until the top of the pepper comes off (kind of like a hat). Slice each bell pepper in half from top to bottom and remove any seeds with your fingers and discard them. Place them in a dish as well.

For the zucchini, cut a bit of the ends off then you can either cut it in half or quarters lengthwise (so you have long pieces). If you have a thinner zucchini you may want halves; for a thicker zucchini I would definitely recommend quarters. Place the zucchini in a dish.

The mushrooms require very little prep. You can remove the stems if you like - they do tend to soak in more of the marinade that way - but it's not necessary. Place them in a dish as well.

Now you need to make the marinade and cover the vegetables in it. First make sure they're in a single layer in the dish or plastic ziploc bag. Again, you may need more than one dish or bag to do this.

Make the marinade by pouring the balsamic vinegar and oil into a measuring cup, then add the kosher salt and ground black pepper into it. Stir with a whisk until it's combined. If it doesn't want to combine try pouring it into a container with a lid and shaking it.

Next pour the marinade over the veggies. Use your hands to help coat all of the veggies in the marinade; you will likely need to flip the onion slices and bell peppers several times to get them completely coated.

If using a dish, cover with a lid or piece of plastic wrap, or if using a plastic bag just squeeze out as much air as you can and seal the bag. Marinate the veggies in the fridge for 30 minutes to 1 hour, removing them 10 minutes before placing them on the grill to let them warm slightly - meaning they'd only be in the fridge for 20 to 50 minutes.

When the marinated veggies are on the counter warming slightly, go ahead and preheat your grill to between 375 and 400 degrees F. Once the grill comes to temperature, use tongs to place the veggies directly on the grill grates and close the lid. Keep the marinade the veggies were in to either brush or drizzle on the grilled veggies once they're done.

The different veggies will have different grilling times, as outlined below. They're ordered from shortest to longest total cooking time.

Zucchini: 2 to 3 minutes on the first side, then another 2 to 3 minutes on the second side.

Asparagus: 2 to 3 minutes on the first side, then another 2 to 3 minutes on the second side (same as zucchini).

Bell Peppers: 4 minutes on the first side, then another 2 to 4 minutes on the second side.

Mushrooms: 4 minutes on the first side, then another 3 to 4 minutes on the second size.

Onions: 5 minutes on the first side, then another 4 to 7 minutes on the second side.

When the veggies are done cooking, set them on a platter and drizzle or brush any leftover marinade on top, if desired, then serve!