Melt butter in a large skillet over medium-high heat; add purple onion, and sauté until tender. Add zucchini, and sauté 10 minutes or until tender. Stir in chopped green onions.
Process sautéed vegetables, broth, and next 3 ingredients in batches in a blender until smooth, stopping to scrape down sides. Stir in salt and pepper. Cover and chill. Top each serving with 1/3 cup Fresh Vegetable Salsa.