Preheat the oven to 500°F and line a large baking sheet with parchment paper. 

Place the tomatoes, onion quarters and chiles on the baking sheet and drizzle with the olive oil. Using your hands, toss and rub the vegetables, making sure that they are evenly coated with the oil. Bake in the upper third of the oven until the skins are blistered and charred in places, 20 to 25 minutes. Turn the vegetables over and continue to cook until blistered and charred in places on the second side, 15 to 20 minutes longer. Remove from the oven and set aside to cool to room temperature. 

Remove the skins and stems from the peppers and discard. Remove the skins from the tomatoes. Transfer the peppers, tomatoes, onion pieces and all remaining ingredients to a food processor and pulse until a coarse yet blended texture is achieved. Taste and adjust the seasoning, if necessary, then set aside at room temperature until ready to serve. Salsa may be refrigerated up to 1 week in advance (and returned to room temperature before serving).