Begin by preparing the mushroom marinade. In a bowl, whisk together the olive oil, balsamic vinegar, tamari, sea salt, and black pepper.

Remove the stems from the portobello mushrooms and gently clean them with a damp cloth or paper towel.

Place the mushrooms in a shallow dish and pour the marinade over them. Use a brush or spoon to ensure the mushrooms are evenly coated.

Allow the mushrooms to marinate for at least 15 minutes, or up to 1 hour if time permits. This will give them plenty of time to absorb the flavors.

Meanwhile, preheat your grill or grill pan to medium-high heat.

Once the mushrooms are done marinating, place them on the grill and cook for 4-5 minutes per side, or until they are tender and lightly charred.

While the mushrooms are grilling, toast your hamburger buns on the grill or in a separate toaster.

Once the mushrooms are cooked, you can add your desired toppings. Start by placing a mushroom on the bottom half of each toasted bun.

Add a generous amount of lettuce, sliced tomato, sliced red onion, and pickles on top of the mushroom.

Finish off your mushroom burger with your favorite condiments, such as mayo, ketchup, or mustard.

Place the top half of the toasted bun on top of the condiments, and your homemade portobello mushroom burger is ready to be enjoyed!