Stir together couscous and boiling water in a large, heatproof bowl. Cover with plastic wrap, and set aside for 10 minutes.
Meanwhile, heat olive oil in a skillet over medium heat. Stir in onions and garlic, and cook until the onion has softened and turned translucent, about 5 minutes. Add the diced Roma tomatoes, and cook until the tomatoes release their juice and the mixture begins to thicken.
Fluff the couscous with a fork, then fold in the tomato mixture and cheese. Serve immediately as the cheese is melting.
