1. Preheat oven to 425°.
2. Place corn and potatoes on a jelly-roll pan. Drizzle vegetables with 1 tablespoon oil; toss to coat. Bake at 425° for 30 minutes or until potatoes are tender. Place mixture in a large bowl. Combine tarragon and next 5 ingredients (through pepper) in a small bowl, stirring with a whisk. Gradually add remaining 1 1/2 tablespoons oil, stirring constantly with a whisk. Drizzle potato mixture with dressing; toss gently to coat.
3. Heat a large skillet over medium heat. Coat pan with cooking spray. Add onion and zucchini to pan; cook 4 minutes or until lightly browned, stirring occasionally. Add zucchini mixture and tomatoes to potato mixture; toss gently to combine.