Remove and finely chop the mushroom stems. Put aside. With a spoon, scrape the inside of the mushroom (the black part on the underside of the mushroom cap) and discard it. Set aside the mushrooms.
In a large bowl, combine olive oil, balsamic vinegar, Worcestershire sauce, whole grain mustard.
Brush the portobello mushroom with the marinade and coat well. Marinade for at leaat 30 minutes.
Preheat the BBQ over medium high heat. Or preheat the oven to 400 F˚
In a skillet over medium heat, add the chopped mushroom stalks, tomatoes, bell pepper and onion. Season with salt and pepper. Sauté over medium-high heat for about 2 minutes. Add the wine and quinoa . Bring to a boil and let reduce almost dry. Add the croutons, set aside.
Remove the mushroom caps from the marinade and place them on a plate. Season with salt and pepper. Fill with stuffing and sprinkle with cheese. Place on the barbecue grill or in the oven and cook for about 20 minutes.
Sprinkle with fresh basil and voila, Bon appétit !