Preheat a grill pan to medium high heat or prepare outdoor grill.
Turn the oven on moderate heat. Place the hollowed bread in oven to crisp, 5 minutes.
In a small bowl, whisk together sherry vinegar, mustard, Worcestershire sauce, extra-virgin olive oil and garlic. Place mushrooms in a shallow dish and pour marinade over the caps. Turn caps in marinade and season with salt and pepper. Let stand 10 minutes. Prep your parsley and spinach.
Grill mushrooms 4 to 5 minutes on each side and remove to a cutting board a few at a time. Thinly slice the mushrooms and transfer back to the dish you marinated them in and add parsley and spinach as you go, layering hot mushrooms with the herb and greens. Once all the hot sliced mushrooms combine with the spinach, the greens will wilt up a bit. Toss the salad and adjust the salt and pepper, to your taste.
Pile the salad into crispy bread and top with manchego cheese and red peppers of choice then set bread tops in place.