In a large shallow baking dish, whisk together balsamic vinegar, gluten-free tamari, grapeseed oil, vegan Worcestershire sauce, liquid smoke, minced garlic, granulated onion, salt, and fresh cracked pepper.

Gently clean the portobello mushrooms with a dry brush, then add them to the marinade and let them sit for about 10-20 minutes, flipping halfway.

Preheat your grill or grill pan over medium-high heat. Lightly brush with oil.

Place marinated portobello mushrooms in the pan or on the grill and cook for 4-5 minutes.

Flip the mushrooms and cook for another 4-5 minutes until tender and charred.

Serve immediately while hot, either alone or with sides.