Insert skewers in tomatoes and lay on open flame or cut in half. Lay cut side down on baking sheet and broil. Char until skin is blackened and peeling. Remove from flame and rest on plate. Peel off charred skin. Using a fork mash tomatoes, and add salt. In a mortar smash garlic, peppers and cilantro. Mix with pureed tomatoes. Heat some of the oil in a saucepan and caramelize onion. Add heated oil caramelized onion mixture to tomatoes.