Melt butter in large pot over medium heat. Saute onion, zucchini, celery and carrot for 5 minutes, stirring occasionally. Add in grated garlic and cook another 5 minutes. Sprinkle in flour, stir to coat veggies and cook 2 minutes.
Whisk in water and bring to boil over medium high heat to thicken. Reduce heat to low and add in milk and seasonings. DO NOT bring the soup to boil after the milk has been added to ensure soup doesn't curdle.
Slide whole chicken breasts into hot liquid and poach 10-15 minutes until fully cooked. Remove and shred chicken, then slide back into chowder. Stir in frozen corn to warm through, then serve immediately.
*or chicken broth crystals/powder enough for 8 cups of liquid