Fill a pot with water and place a steamer basket on top. Place the sweet potatoes in the basket and bring to a low boil over medium-high heat. Once boiling, reduce to a simmer and cover. Cook for 50 to 60 minutes, until the potatoes are fork tender and cooked through.
Meanwhile, mix together the softened butter, miso paste and chopped nori until well combined and then set aside.
Heat a grill over medium-high heat.
Once the potatoes are done cooking, remove and let cool slightly before slicing in half lengthwise. Lightly spray with avocado oil, if using.
Place the potatoes cut side down on the grill and cook for four to five minutes, until charred. Rotate the potatoes to create crosshatch grill marks and cook for another four to five minutes.
Add the potatoes to a large plate or platter and top with some of the butter, chives, sesame seeds and lime wedges (if using).
