Wash the Japanese sweet potatoes thoroughly under running water to remove any dirt.
Pat the sweet potatoes dry and cut them into approximately 1/2-inch thick rounds or wedges, depending on your preference. Keeping the pieces similar in size will ensure even cooking.
In a mixing bowl, combine the vegetable oil, soy sauce, mirin, honey or maple syrup, sesame oil, grated ginger, minced garlic, chili flakes, and a pinch of salt. Whisk marinade until well combined.
Place the sweet potato pieces in a large resealable bag or a shallow dish. Pour the marinade over the sweet potatoes, ensuring they are evenly coated. Seal the bag or cover the dish and let the sweet potatoes marinate for at least 30 minutes, or up to 2 hours for more flavor.
Once your potatoes are marinated, preheat your BBQ grill to medium-high heat.
Once the grill is heated, place the rounds on the grill, turning them over after 6-8 minutes, to cook on the other side for another 6-8 minutes. You can use the remaining marinade to put on the potatoes while grilling.
Take them off once their cooked through with grill marks. Enjoy!
