Harissa, the spicy chile sauce from Northern Africa, is a traditional accompaniment for couscous; it's available at most Middle Eastern groceries. Satisfying Vegetarian Recipes
Preheat the oven to 425°. Arrange the bell peppers on a baking sheet and roast for about 35 minutes, turning occasionally, until the skins are blistered all over. Transfer the peppers to a bowl, cover with plastic wrap and let steam for 15 minutes.
Peel the green peppers and discard the cores, seeds and ribs. Cut the peppers into thick strips and put them in a medium bowl. Working over a strainer set over the bowl to catch the juices, peel the red peppers and discard the cores, seeds and ribs. Cut the red peppers into thick strips and add to the bowl.
Heat the oil in a medium saucepan. Add the garlic and cook over moderately low heat, stirring, until translucent, about 4 minutes. Add the tomatoes and salt and simmer until slightly thickened, about 10 minutes. Add the pepper strips and red pepper juices and simmer gently over low heat until thickened, about 30 minutes. Stir in the harissa; serve warm.
The roasted peppers can be refrigerated overnight. Rewarm over low heat.