Boil the sweet potatoes in salt water for about 7-10 minutes, until they are fork tender. Drain. In a saute pan, cook the tofu, corn oil, sea salt, and tamari for about 7-10 minutes. You don't want to brown the tofu, just cook it. Add the minced kale so that it cooks during the last minute, then remove from heat. Let tofu and sweet potatoes cool to room temperature. In a bowl, mix the potatoes, tofu, onion, celery, mayonnaise, and mustard all together. Refrigerate and serve chilled.