Toss the sweet potatoes with 2 tablespoons miso in a large bowl.
In a cast-iron skillet over medium-low heat, melt enough coconut oil to coat the bottom, about 2 tablespoons. When the oil is hot, add the sweet potatoes and sear on one side until dark brown, 3 to 4 minutes. Flip and repeat on the other side, cooking until tender, about 5 minutes more. Evenly spoon the remaining miso on top of each piece of potato and cook for 1 minute more. Serve immediately.
Cook¿s Note: If you find that the potatoes are not cooked through, finish cooking them in the oven at 350 degrees F until tender, 5 to 10 minutes.