1. Bring 1-1/2 cups water to boil in base of steamer. Place green onions, asparagus, zucchini and broccoli on steamer rack. Cover and cook until vegetables are just tender, about 5 minutes.
2. Transfer vegetables to plate and cool. Reserve steaming water. Add enough milk to reserved steaming water to measure 2 cups liquid (about 1 cup)
3. Dice vegetables and then set aside. Melt butter in heavy large skillet or Dutch oven over medium-low heat. Add onion and celery and cook until tender, stirring occasionally.
4. Meanwhile, bring milk mixture to simmer. Stir flour into skillet. Bring to boil, stirring constantly. Add diced vegetables to soup and heat through.Season with salt and pepper. Garnish with cilantro and serve.