-
Cut the mushroom caps into very thin slices. Heat 1 tablespoon of the oil in a large skillet over medium-high heat. Working in batches, add the mushroom slices and sear on both sides. Season with salt and pepper to taste. Transfer the cooked mushrooms to a plate and cook the remaining mushrooms slices. When all the mushrooms are cooked, combine them all in the skillet and set aside.
-
In a small bowl, combine the vinegar, soy sauce, and mustard, stirring to blend. Pour the mixture over the mushrooms, turning to coat. Set aside to cool.
-
In a food processor, combine the white beans and garlic and process to a paste. Add the tahini, sun-dried tomatoes, lemon juice, water, and salt and pepper to taste. Process until smooth. Set aside.
-
Use a serrated knife to cut the bread in half horizontally. Use your hands to pinch out the soft center of the bread from inside both halves of the loaf to make room for the filling.
-
Spread the white bean mixture inside the both halves of the loaf. Remove the mushrooms from the marinade and layer them over the white bean mixture, alternating with layers of the roasted peppers, artichoke hearts, spinach, tomato, and olives. Drizzle with the remaining marinade and season with salt and pepper to taste. Replace the top half of the loaf and wrap the entire loaf tightly in plastic. Place the sandwich on a large plate and top with another plate, lid or pan. Weigh the top down with canned goods. Refrigerate for at least 4 hours or up to 12 hours. When ready to serve, unwrap the sandwich and cut it with a serrated knife into 4 four to 6 six wedges.