Balsamic Vinegar. Tang. Depth of flavor. Delicious.
Soy Sauce. That umami somethin’ somethin.’
Spices. First, garlic powder. Because 1) minced garlic can burn and 2) sometimes I’m too lazy to mince garlic. Second, black pepper. Not enough to make these grilled portobello mushrooms spicy. Just enough to wake up their flavor and make you wonder why you can’t stop eating them. Third, cayenne. Optional but encouraged.
Rosemary. A hearty herb that can stand up to the mushrooms without overpowering them. Fresh thyme would be tasty too.