Bring a large pot of salted water to a boil over high heat. Cook the corn kernels until just tender, about 1 minute; transfer with a slotted spoon to a colander. Add the beans to the boiling water and cook until crisp-tender, about 3 minutes; transfer to the colander.
Keep the water at a boil while you toast the couscous in two batches in a dry skillet over medium heat, stirring, until
golden-brown, about 4 minutes. Cook the couscous in the boiling water until tender, about 10 minutes. Drain the couscous and toss it immediately with 1 Tbs. of the olive
oil. Let the couscous cool completely in the refrigerator.
Put the lemon juice in a small bowl and gradually whisk in the remaining 1/2 cup of olive oil. Taste and season with salt, pepper, and additional lemon juice or olive oil as needed.
Put the cooked and cooled couscous in a large serving bowl and toss to
break up any clumps. Add the corn, green beans, zucchini, goat cheese,
basil, and the vinaigrette and toss. Taste and season as needed with
more salt and pepper. Serve within an hour or two of making.