Puree 2 tomatoes, 2 tablespoons each tomato paste and water, 1 tablespoon red wine vinegar, a 2-inch piece of peeled ginger, 1 garlic clove, 3/4 teaspoon kosher salt and 1/4 teaspoon ground turmeric. Heat 2 tablespoons olive oil in a skillet over medium heat; add the puree and cook, stirring, until thickened to a paste, 12 minutes. Add 1 cup water and bring to a simmer. Remove from the heat and stir in 1 cup couscous; cover and let sit 10 minutes. Fluff with a fork, season with salt and top with chopped cilantro.