Heat oven to 425°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. Arrange onion pieces in baking dish. Bake 10 minutes. Add bell peppers and mushrooms to onions; spray with cooking spray and sprinkle with salt. Bake 15 minutes. Stir in tomatoes. Bake about 5 minutes longer or until vegetables are tender.
Meanwhile, cook and drain linguine as directed package.
Stir pesto into roasted vegetables. Place linguine on large serving platter. Top with vegetable mixture and cheese.