In a large (preferably nonstick) skillet set over medium heat, lay in the tomatoes and chiles (cut side down) along with the garlic. When richly browned underneath, 4 or 5 minutes, flip and dry-roast the other side.
In a large mortar (or food processor or blender), pound (or whir) the chiles and garlic into a coarse-textured puree. If using a processor or blender, add the tomatoes and their juices and pulse into a coarse, rich-textured salsa. If using a mortar, crush the tomatoes in a piece at a time.
In a very large (12-inch) skillet or very large (4-quart) saucepan over medium-high, heat the oil. Add the tomato salsa and stir for 2 or 3 minutes, until rapidly boiling. Add the broth, bring back to a boil, then taste and season with salt, usually about 1/2 teaspoon, depending on the saltiness of your broth. Add the mussels or clams to the boiling broth and cook until they begin to open, about 2 minutes. Add the scallops and cook for a minute longer. Finally, add the shrimp and rice. As soon as the mixture returns to a rolling boil, spoon into warm, large bowls. Serve with lime wedges.