In a large saucepan, heat the olive oil over medium heat. Add onions and saute until softened, approximately 5 minutes. Season with salt and pepper. Add thyme, zucchini, squash, and mushrooms. Saute for 5 to 10 minutes. Add garlic and stir. Add tomatoes, stock, and garbanzo beans. Let simmer for 5 to 10 minutes. Add more stock if dry. Add 1/4 cup parsley, red wine vinegar, and basil. Taste and adjust seasonings.
Add the raisins and remaining parsley to the prepared couscous, and stir to combine. Plate couscous and spoon stew over the top.