Your layer's order is critical so your sandwich does not get soggy.
Start with half the fresh spinach. You do not want cooked spinach (it will cook in the oven).
Put the spinach into the corners of the bread base, making a layer of spinach on the bottom. Push down to pack in.
=Then add the tomato slices, slightly overlapping each other.
Now, add grilled/sautéed portobello mushrooms. Again, cover the bottom, pushing them into the sides in a single or double layer.
Then add the red peppers; again, cover the base and push into the corners. It should be a single layer. Brush with dressing.
Then layer onions the same way. Brish with dressing.
Layer the summer squash; brush with dressing
Layer the zucchini; brush with dressing.
Top with the rest of the fresh spinach.
The top has a hole, so don't worry if the spinach is falling out of the top.
*It should be overflowing.
Add the top of the bread, brush with dressing on the inside, and push any remaining spinach back inside the bowl.
*The fresh spinach is a barrier for sautéed vegetables, so they do not make your bread soggy.
Wrap and BakePre-heat over t0 400 degrees
Wrap the entire bowl, top, and all in aluminum foil.
Place on a baking sheet.
Bake for 20 minutes.
Remove from oven.