Heat 1 tablespoon olive oil in a Dutch oven over medium heat. Sauté the 2 diced onions for about 5 minutes, until golden brown and soft.
Stir in the 4 chopped garlic cloves, 0.5 pound chopped sweet mini peppers, 1/2 cup chopped sun-dried tomatoes, and 2 tsp Italian seasoning. Cook for 1 minute, stirring continuously.
Add the 15 ounces diced tomatoes, 1 cup low-sodium vegetable stock, 1 tablespoon balsamic vinegar, and 30 ounces chickpeas. Bring the stew to a boil, then reduce the heat and simmer for 15 minutes.
Over the last couple of minutes, stir in the 4 cups spinach. Taste and season with Kosher salt and ground pepper.
Serve the stew with 1/2 cup shaved parmesan cheese and fresh chopped parsley or basil, if desired.