Melt butter in large pot over medium heat. Add white part of scallions, carrots, potatoes, salt, pepper, and garlic powder. Cover and cook 8 minutes, stirring occasionally, until vegetables are slightly soft but not browned.
Add flour to pot and mix into vegetables. Add water stiring at same time to dissolve the flour. Bring to a boil, reduce heat, cover and simmer 10 minutes or until vegetables are almost tender.
Stir in green part of scallions, milk, green beans, corn, peas, and thyme. Bring to a boil, reduce heat and simmer uncovered 5 to 10 minutes until vegetables are tender. (Make sure heat is not to high or milk will scorch and get yucky.).