Slice the yellow squash on the diagonal into quarter inch thick slices. Sprinkle with the fine sea salt and set aside for 10-15 minutes.
While the squash is sweating, preheat your grill or grill pan to medium high heat. Preheat your grill basket or topper if using. Slice the onions into quarter inch-thick slices. Cut the tops and bottoms off of the bell peppers and then cut into 8 wedges. Remove the seeds and membranes, and spray or brush them with a very light layer of olive oil.
Spray your grill or grill topper with nonstick spray. Add the peppers to the grill or grill basket. Close the lid, or if you are using a grill pan, cover the peppers with a lid or a sheet of foil (it doesn’t have to be sealed). Cook for 10 minutes, then add the onions. Continue to grill, turning every 5 minutes or so, until the peppers and onions are soft and have grill marks. Thicker peppers may take a bit longer to cook.
Use a paper towel to blot the yellow squash dry, and re-spray your grill with nonstick spray if needed (the yellow squash does have a tendency to stick). Spray or brush the squash slices lightly with olive oil and add to the grill. Cook, turning only once, until the squash has nice grill marks but aren't floppy, about 3-4 minutes per side.
Slice the peppers into smaller strips, and season the cooked onions and peppers with just a bit of salt and pepper to taste.
Use a bread knife to carefully slice your ciabatta loaf in half lengthwise and brush the insides with extra virgin olive oil. Add the bread sliced-side down and cook until you get grill marks on one side, pressing down with a spatula if necessary to get good contact. Remove to a cutting board.
Assemble your sandwiches. Spread grilled ciabatta tops with goat cheese and the bottoms with tapenade. Layer the yellow squash, bell pepper, and onions (pull the rings apart to spread them out). Top with arugula, and drizzle the whole thing with balsamic glaze and a couple cranks of black pepper. Top with the ciabatta top and cut into four quarters, then cut the quarters in half diagonally. Enjoy!
Notes
Salting the yellow squash is optional, but helps the squash stay crunchy as it cooks.
You can substitute jarred roasted red peppers. Be sure to blot them off with a paper towel before adding to your sandwich (no need to cook them).
If your tapenade is extra juicy, scoop it out with a fork and allow some of the oil to drain away so that it doesn’t saturate your sandwich.