Start by whisking together the olive oil, minced garlic, dried oregano, sea salt, tamari, balsamic vinegar, ground black pepper, and fresh lemon juice in a bowl.
Ensure all ingredients blend seamlessly. This marinade will work its magic, adding flavor and tenderness to your portobello caps.
Take the portobello mushrooms and submerge them in the marinade. Make sure they’re well coated. Allow them to soak for at least 30 minutes. I recommend letting them marinate longer if you can. An hour works wonders, allowing all those flavors to seep in!
While your mushrooms are marinating, fire up the grill. Aim for medium heat, around 350°F to 400°F. If using a charcoal grill, wait until the coals are glowing and have a coating of ash.
Remove the mushrooms from the marinade and place them gill-side down on the grill. Grill for about 5-7 minutes until you see nice grill marks.
Flip the mushrooms, and grill for an additional 3-5 minutes. You’ll know they’re done when they’re tender and juicy.
Once grilled to perfection, remove the mushrooms from the grill and let them rest for a couple of minutes. Slice them up or serve them whole on a plate. You can drizzle any leftover marinade over them before serving.