Cut chicken thighs into 1.5-inch pieces and pat dry with paper towels. Season lightly with salt and pepper. Whisk soy sauce, sesame oil, garlic, ginger, and brown sugar in a medium bowl until sugar dissolves. Add chicken, toss to coat, and marinate for 10 minutes.

Rinse jasmine rice until water runs clear. Bring 2 cups water to a boil in a medium saucepan. Add rice, stir once, reduce to lowest heat, cover tightly, and cook undisturbed for 15 minutes. Turn off heat and keep covered 5 more minutes. Fluff with a fork.

Heat neutral oil in a large Dutch oven over medium-high heat until shimmering. Add marinated chicken in a single layer, leaving excess marinade in the bowl. Cook undisturbed 3 to 4 minutes until golden brown. Flip and cook another 3 to 4 minutes until internal temperature reaches 165 degrees F.

Pour in chicken broth and rice vinegar, scraping up all browned bits from the bottom. Bring to a boil then reduce to a gentle simmer. Stir cornstarch mixture to recombine, then slowly drizzle into the simmering broth while stirring. Broth will thicken within 1 to 2 minutes. Simmer 5 more minutes.

Taste and adjust seasoning with salt, pepper, or additional soy sauce. The broth should taste slightly bolder than needed since the unsalted rice will balance it in the bowl.

Divide rice among 4 deep bowls. Ladle chicken and broth generously over each serving. Top with sliced green onions and serve immediately.