Combine 1/4 cup dressing, rosemary, 2 teaspoons olive oil, 1/2 teaspoon salt, and ground red pepper, stirring well with a whisk. Combine acorn squash, fennel, and onion in a large bowl. Add dressing mixture, tossing to coat. Spread vegetable mixture evenly in a roasting pan coated with cooking spray. Roast at 450° for 45 minutes or until vegetables are tender, stirring occasionally. Set aside.
Place salad greens in a bowl. Add 1/4 cup salad dressing, 1 1/2 teaspoons olive oil, 1/4 teaspoon salt, and balsamic vinegar; toss well. Add roasted vegetable mixture, tossing gently.