Preheat a grill to medium-high heat (375 to 450 degrees)

Clean the Portobello mushrooms and remove the stems.

Drizzle the gill sides with the olive oil and use your hands to rub all over the mushrooms, including the bottoms.

Drizzle the gill sides with balsamic vinegar, sprinkle with kosher salt, and add several grinds of black pepper.

Place the mushrooms directly on the grill grates gill side up and grill 10 to 14 minutes until tender and juicy. Liquid will pool in the cap.

Flip the mushrooms (this drains the liquid into the grates) and cook for an additional 2 to 3 minutes until browned.