To make the dressing. Combine all ingredients in a glass jar and whisk until smooth. Taste and adjust the salt and pepper.In a large bowl, toss the zucchini and peppers with 1/2 of the dressing. Let sit 10 minutes. Preheat the grill or grill pan to high. Rub each half of the bread with olive oil. Grill the bread, cut side down, for 3-5 minutes or until light grill marks appear. At the same time, grill the peppers and zucchini until softened, 3-4 minutes per side. Remove everything from the grill. Working with the bottom piece of bread, drizzle with a couple spoonfuls of the dressing, then layer on the vegetables, burrata, and provolone. Add the spinach and herbs. Drizzle the remaining dressing over everything. Add the top half of the ciabatta and gently push down on the sandwich. At this point, you can slice the sandwich and serve warm or wrap the sandwich tightly and place in the fridge for 1 hour or up to 1 day. Before serving, cut into 4-6 sandwiches.