1. Heat the broiler to high and arrange a rack in the middle. Line a baking sheet with aluminum foil, then place tomatoes skin side up on the baking sheet. When the broiler is hot, broil tomatoes until skins are slightly charred. Remove tomatoes from the oven; set aside. Turn oven to 350°F. 2. Place tomatoes in a large stainless steel pan over high heat. Add chiles de arbol, pasilla peppers, salt, sugar, water, and stir to combine. Bring to a boil, reduce heat to low and simmer, stirring often, until slightly reduce and thickened, about 20 minutes. 3. Meanwhile, toast pumpkin seeds on a baking sheet until just browned, about 10 minutes. Remove baking sheet form oven; set aside. 4. Add vinegar to tomato mixture and cook 1 minute. Place mixture in a blender, add toasted pumpkin seeds, and blend until smooth. 5. Pour salsa into a container and stir in scallions and cilantro. Refrigerate until chilled before serving, about 3 hours.