Heat the remaining 1 tablespoon of olive oil in the skillet. Add the shrimp and scallops, season with salt and pepper and cook over moderate heat for 1 minute, then turn and cook for 30 seconds longer. Add 1 cup of the romesco sauce and bring to a simmer; if the sauce seems too thick, add 2 tablespoons of water to loosen it. Add the squid and cook just until it turns opaque, about 2 minutes. Remove from the heat, season with salt and stir in the parsley. Transfer to a platter and serve. Pass the remaining romesco sauce at the table or refrigerate for another use.