1. Preheat oven to 450°.
2. Combine beans and oil in a large zip-top freezer bag; seal and shake well. Add garlic powder and salt; seal and shake to coat.
3. Arrange seasoned green beans evenly on 2 large baking sheets coated with cooking spray.
4. Bake at 450° for 24 minutes, using 1 oven, switching pan positions after 12 minutes.