Divide the noodle mixture evenly between four large squares of parchment paper. Sit a salmon fillet on top, followed by 1 tablespoon of soy sauce over each one. Gather the edges of parchment paper up over the salmon, scrunching them together to enclose securely. These can be prepared to this stage up to a day in advance and kept refrigerated. If being frozen, make sure you defrost them thoroughly before cooking.