Heat large saute pan on grates of the grill over medium heat. Add couscous and toast until lightly golden brown.
Bring 6 cups of water to a boil over high heat, add 1 tablespoon salt and toasted couscous and cook until al dente. Drain well and place in a large bowl. Add grilled vegetables, olives, basil, and vinaigrette and toss until combined; season with salt and pepper. Let sit at room temperature for 30 minutes before serving or cover and refrigerate.
Whisk shallot, juice, zest, vinegars, and salt and pepper together in a small bowl. Slowly whisk in oil until emulsified.