In a large saucepan with a lid, bring 1 cup salted water to a boil. Add green beans. Cover, and cook over medium-high until crisp-tender, 4 to 5 minutes. Add corn and shrimp; stir to combine. Cover, and cook until shrimp are opaque throughout, about 2 minutes.
Add couscous, and stir to combine; cover, and remove from heat. Let stand 5 minutes. Add basil, vinegar, and oil; season with salt and pepper, and fluff with a fork.