1. Cut each baguette in half cross-wise, then split lengthwise and remove some of the soft insides (discard or use in another dish).
2. Preheat a grill pan to medium high heat or prepare outdoor grill.
3. Preheat oven to 325°. Place the hollowed bread in oven to crisp for about 5 minutes.
4. 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.
5. Grill mushrooms 4 to 5 minutes on each side and remove to a cutting board a few at a time, but keep them warm. Thinly slice the mushrooms and transfer back to the dish you marinated them in and add parsley and spinch as you go, layering the hot mushrooms with the parsley and spinach. Once all the hot sliced mushrooms combine with the spinach, the greens will wilt a bit. Toss the salad and adjust the salt and pepper to your taste.
6. Pile the salad into crispy bread and top with manchego cheese and red peppers of choice, then set bread tops in place.