A simple, zesty marinade enhances the earthy meatiness of portobellos, and grilling them deepens the rich flavor.
In a large bowl or a zip-top bag, combine the olive oil, Worcestershire sauce, salt, pepper, garlic powder and lemon juice. Add the mushrooms and marinate for 30 minutes to 1 hour.
Heat a grill pan over medium-high heat. Remove the mushrooms from the marinade, shaking off any excess, and transfer to the grill pan. Cook until browned and grill marks appear, 2 to 3 minutes per side.