Rinse and scrub the potatoes well. Slice larger ones in half so everything cooks evenly.
In a large skillet over medium heat, add avocado oil. Toss in the potatoes and let them get a bit golden—about 5 to 7 minutes.
Add garlic and stir just until fragrant, maybe 30 seconds.
Pour in soy sauce, mirin, brown sugar, and water. Give it a good stir.
Bring it to a simmer, cover, and cook for 15–18 minutes. Stir occasionally.
Once the sauce thickens and the potatoes are tender, uncover and let it reduce a bit more, around 5 minutes.
Drizzle in sesame oil, sprinkle with sesame seeds, and toss in chopped green onions if you like.
Serve warm or at room temp. Eat straight from the pan—I won’t judge.