Wash mushrooms and set aside - either in a wide, flat dish or in a gallon Ziplock bag. Set aside.
Combine avocado oil, onion powder, minced garlic, ground thyme, balsamic vinegar, and liquid aminos in a small bowl; mix thoroughly.
Pour your marinade over the mushrooms and ensure they are evenly coated. Allow them to marinate for 5+ minutes before flipping and marinating for another 5+ minutes.
Turn grill to low-medium heat. Once it is hot, place mushrooms on the grill and drizzle with remaining marinade. Cook for several minutes per side. They are done when they have shrunk slightly and the edges are slightly crisp.
Serve hot on a bun with condiments or on a bed of lettuce. Can be refrigerated and sliced before serving in a salad.
Feel free to marinate your mushrooms for longer than 10 minutes; half an hour is great, and several hours is spectacular.