Combine the couscous, cumin, and salt in a large bowl. Stir in the boiling water and seal with plastic wrap. Set aside for 10 minutes.
While waiting for the couscous, cook the unpeeled garlic clove in a small skillet over medium-high heat until toasted and the skin has turned golden-brown. Peel the garlic and mince. Stir the garlic into the couscous along with the black beans, corn, onion, cilantro, jalapeno pepper, olive oil, and lime juice. Serve warm or allow to cool.