Preheat oven to 425.F. Roast potatoes until tender. Let cool before proceeding.
Whisk together the maple syrup, soy sauce, miso, sesame, oil, vinegar, pepper flakes, and water. Set aside.
Heat oil in a large pan over medium-high heat. Chop sweet potatoes into 2" chunks and add to pan. Cook until deeply browned on all sides.
Reduce heat to medium, pour sauce over potatoes, and continue to cook, basting potatoes, until sauce is thickened.
Didn't add any flavor; just tasted like plain sweet potatoes.