In a large bowl, toss the prepared portobello mushrooms, red bell peppers, and zucchini with a few generous drizzles of olive oil, 1 tablespoon dried oregano, and salt and pepper to taste.
Heat a grill to medium-high. Grill, for about 10-12 minutes, or until charred and tender on both sides. To get the grill marks, grill each side undisturbed before turing. Transfer to a plate and set aside. Optional: brush with pesto on each side as the veggies grill for extra flavor.
Cut the large loaf of ciabatta into 4 and cut in half lengthwise.
Build the sandwiches: Spread some goat cheese on each cut side of the sandwich. Top the bottom half with some arugula or mixed greens, followed by the grilled red bell peppers, grilled zucchini, and grilled portobello. Top the sandwich with the top half of the ciabatta.