Remove the seeds from the pepper, and chop into strips about 1 to 2 inches long. Cut the eggplant crossways into rounds about 1/3 to 1/2 inch thick, and cut each one into 6 to 8 even chunks. Peel the onion, and chop into 8 portions. Trim the zucchini, and cut into thick slices.
Heat grill pan over a high heat with a generous splash of olive oil. When it is very hot, add all the vegetables to the pan. Press down occasionally to get grill lines across them. Turn occasionally to prevent burning. Cook for about 15 minutes, or until the vegetables are evenly browned and cooked through.
Stir broad beans into the vegetables. Add chopped tomatoes, and vinegar. Simmer for a few minutes while the couscous is prepared.
Place couscous into a medium bowl. Add boiling vegetable stock, and stir with a fork. Keep lifting the couscous occasionally to prevent it sticking. It only takes 2 to 3 minutes to become soft. Place couscous in a large bowl or serving platter, and serve the vegetables on top.