To prepare dressing, combine first 8 ingredients in a large bowl; stir well with a whisk. Set aside.
To prepare shrimp, combine 2 teaspoons olive oil and next 6 ingredients (through shrimp) in a large bowl; toss well. Thread about 5 shrimp onto each of 6 (8-inch) skewers. Place skewers on a grill rack coated with cooking spray; grill 3 minutes or until done.
To prepare salad, add spinach, mushrooms, and onion to vinegar mixture; toss gently to coat. Serve with shrimp skewers.