Put the portobello mushroom caps in a bowl or shallow dish and add the olive oil, balsamic vinegar, and half of the salt and pepper; marinate for at least 30 minutes.

Cook the bacon in a skillet at medium-low heat until crispy, flipping over a couple of times to evenly cook each side. Set aside for later use as a topping.

Turn the grill on medium-high heat (about 200-300 degrees). In a bowl, mix together the ground beef, garlic powder, onion powder, Worcestershire sauce, and the rest of the salt and pepper. Form into a patty, ideally not quite as wide as the portobello “buns.”

Put the portobello mushrooms and the burger on the grill (you may need to do this separately if you are preparing multiple servings). Cook the portobello mushrooms for about 3-4 minutes on each side until they are soft and heated through. The burger will take about 5-6 minutes on each side for medium-rare. Put the cheese on the burger for the last minute of cooking to melt.

Assemble your burger with the bacon and the rest of the toppings between the portobello mushrooms.