If using Israeli couscous, bring 2 1/2 cups water to a boil in a medium saucepan; if using regular couscous, reduce amount of water to 2 1/4 cups. Meanwhile, in a large saucepan, heat olive oil and butter over medium-low heat. Add onions and cook until lightly browned, about 8 minutes. Stir in cumin and cayenne pepper, and sauté for 1 minute more.

Stir in couscous, salt, pepper, and boiling water. Cover and simmer over low heat until tender and water is absorbed, about 10 minutes. Add parsley.