For the glaze: Whisk together the mirin, light soy, olive oil, sugar, ginger, salt and garlic in a small bowl until dissolved and combined.
For the vegetables: Preheat a gas grill or stovetop grill pan to medium-high heat. Brush all the vegetables with the glaze and grill, turning frequently and brushing with more glaze as they cook until crisp-tender, 2 to 3 minutes. Remove the vegetables from the grill and let stand for a few minutes before chopping into bite-size pieces.
For the couscous: Put the couscous in a large bowl. Pour the hot broth over and stir to coat. Cover the bowl with plastic wrap and let stand until the liquid is absorbed, about 5 minutes.
Meanwhile whisk together the light soy, olive oil, sesame oil and lemon juice in a small bowl until combined. Uncover the couscous, pour in about 2 tablespoons of the soy mixture and fluff with a fork. Add half of the cilantro and toss gently.
Spoon the couscous onto a serving platter and arrange the chopped vegetables over and around it. Drizzle more of the soy mixture over the vegetables, if desired, and sprinkle with salt and black pepper. Serve immediately.