Make couscous as directed on package.
Spray 10-inch nonstick skillet with cooking spray; heat over medium-high heat. Add zucchini, yellow squash, bell pepper and onion; spray lightly with cooking spray. Cook about 5 minutes, stirring frequently, until crisp-tender.
Toss couscous, vegetable mixture, pesto and vinegar in large bowl. Serve immediately, or cover and refrigerate up to 2 hours before serving.