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Marinade
Place mushrooms on a medium to hot grill. Cook 6 minutes and flip using tongs, for another 5 minutes or until soft. While mushrooms are grilling, brush with the leftover marinade.
When fully cooked, place mushrooms on a cutting board. Slice into strips. Place watercress on each plate and splash with vinegar. Add salt and pepper. Add mushroom strips. Use grilled mushrooms to make an excellent sandwich with hot sauce.