In a mixing bowl, combine olive oil, balsamic vinegar, garlic powder, onion powder, salt, and pepper.

Place the portobello mushrooms in the bowl, ensuring they are well coated. Let them sit for at least 15 minutes.

Heat your grill or grill pan over medium-high heat.

Place the marinated mushrooms on the grill, gill side down. Grill for about 5-7 minutes, then flip and grill for another 5 minutes.

If using cheese, place a slice on each mushroom during the last minute of grilling.

While the mushrooms are grilling, place the burger buns on the grill, cut side down. Toast them for 1-2 minutes until golden brown.

Start with the bottom half of the bun, add the grilled mushroom, and layer on your desired toppings.

Top with the other half of the bun and serve immediately.