Heat a large pot over medium heat and add sesame oil. Once shimmering, add chicken thighs and brown for 4-5 minutes on each side. Remove from pot and set aside.

In the same pot, combine soy sauce, brown sugar, apple cider vinegar, and water. Add minced garlic, ginger, and black pepper. Stir well to dissolve sugar, then simmer for 2-3 minutes.

Return chicken thighs to the pot, nestling in the sauce. Cover and reduce heat to low, simmer for 30-35 minutes until chicken is fork-tender.

Remove chicken from pot and place on a serving platter. Increase heat to medium-high and simmer sauce uncovered for 5-10 minutes until thickened.

Drizzle the thickened sauce over chicken thighs. Serve with steamed rice or sautéed vegetables and garnish with chopped green onions.