Put the couscous in a large bowl, pass over the hot broth, stir and leave to stand until cool. In the meantime, cut the peppers into 4 cm pieces, discarding the core and seeds, cut the zucchini into thicker rings, and cut the onion into thicker pieces. Put all the vegetables in a bowl, add 2 tablespoons of olive oil and mix everything.
Heat a frying pan and add a layer of vegetables, grill over high heat until it darkens at the edges, place on a plate and grill the rest of the vegetables in the same way. Mix the remaining oil with the rest of the dressing ingredients. Pass the icing over the couscous until it becomes loose, then add the dressing and mix well until all the grains take on the color of the dressing. Add chilled vegetables and coriander and serve at room temperature.