Place the chickpeas, olive oil, lemon juice, tahini, and garlic into the bowl of a food processor fitted with an S-blade. Blend until smooth, stopping to scrape down the sides of the bowl as needed. You can thin the mixture with 1 to 2 tablespoons of water if needed, but you'll want to keep it relatively think so it works to bind the sandwich. Add in the sun-dried tomatoes and pulse until they're finely chopped. Season with salt to taste.
Make the balsamic veggies:
Coat the bottom of a large skillet with olive oil and place it over medium-high heat. Add the bell pepper, zucchini, and onion. Cook, flipping occasionally, until the veggies just begin to become tender and brown in spots, about 2 to 3 minutes. Pour the balsamic vinegar over the veggies and cook until it thickens and forms a sticky coating on the veggies, about 2 to 3 minutes more. Sprinkle with salt and pepper to taste. Transfer the veggies to a plate.
Make the sandwiches:
Slather one side of each bread slices with sun-dried tomato hummus. Pair up the slices and stuff each pair with a fourth of the balsamic veggies and a small handful of arugula or baby spinach.
Wipe out the skillet that you cooked the veggies in, then lightly apply a fresh coating of olive oil and place it over medium heat. Cook the sandwiches, in batches if needed, until browned on each side, about 4 minutes per side.
This recipe makes a nice sized batch of hummus, so use as much as you'd like for the sandwiches. Snack on the leftovers with pita bread and veggies, or store it in a sealed container and it freeze for later.