Cut off tip of each ear of corn. One at a time, stand ears in a wide bowl. With a sharp knife, carefully slice downward to release kernels. Discard cobs; set kernels aside.
In a Dutch oven or 5-quart pot, heat oil over medium. Add onion; season with salt and pepper. Cook, stirring frequently, until onion is translucent, 3 to 5 minutes.
Add broth and 2 cups water; bring to a boil. Add zucchini, green beans, corn, tomatoes (with juice), and orzo; cook, uncovered, until orzo is tender, 8 to 11 minutes. Season with salt and pepper.
Ladle 1 1/2 cups into each of six resealable plastic bags. Store flat in freezer, up to 3 months. Before reheating, thaw in refrigerator.