Heat the oil in a large saucepan over medium heat. Add the onion and garlic; cook and stir until the onion is tender. Stir in the cumin, ginger, turmeric and cayenne pepper; cook for 1 minute.
Pour in the vegetable broth and diced tomatoes with juice; bring to a boil. Stir in the couscous. Reduce heat to low, cover and simmer for 10 minutes.
Remove from heat and fluff with a fork. Stir in parsley if desired.