To make the vinaigrette, whisk together the vinegar, garlic and mustard with salt and pepper to taste. Drizzle the olive oil slowly while whisking to emulsify the dressing. Taste and adjust seasonings as desired.
To marinate the vegetables, combine the vegetables in a shallow dish and pour half the vinaigrette over the veggies and toss. Let them marinate 45 minutes to 2 hours.
Next, either grill or roast the vegetables. If you want to grill on a charcoal or gas grill, place the veggies on the grill or preferably on a grill screen and cook until cooked through and lightly browned, about 10 minutes. They should be tender but not soft. Remove the vegetables as they are cooked - they will cook at different rates. To roast the vegetables, spread all the vegetables except the tomatoes on a baking sheet and roast at 425°F oven for 40 minutes. Add the tomatoes in the last 15 minutes of roasting time.
Let the vegetables cool.
Cut the vegetables into smaller pieces. Cut zucchini and squash into 1/2 inch pieces. Quarter the tomatoes (if the skin peels off, discard it) and cut asparagus into 2-inch pieces. Cut peppers and onions into 1-inch pieces.
While the veggies are cooling, put the broth in saucepan and bring just to a low boil over medium heat. Reduce heat to keep broth warm.
In a saute pan or deep skillet, heat the olive oil over medium-high heat. Add the couscous and stir often until toasted to golden brown.
Add enough stock to cover the couscous by one inch.
Bring to a boil. Cook about 10 minutes until al dente.
Drain couscous and let cool to room temperature.
Add the vegetables, basil, thyme, and parsley to the cooled couscous. Drizzle the remaining vinaigrette over the mixture and toss. Add more salt and pepper to taste.