Place couscous, cumin, and salt in a large heatproof bowl or storage container and pour 1 cup boiling water on top. Cover tightly and let sit until all the liquid is absorbed, about 10 minutes. If the couscous is not quite tender, add an additional quarter cup of boiling water, cover, and let sit for a few minutes longer. Fluff up with a fork. Toss in the beans, corn, onion, cilantro, and jalapeno. Mix in the olive oil and enough lime juice to give the salad a puckery edge. Serve warm or at room temperature.