Place the chicken thigh pieces in a large bowl. Add the cornstarch and toss to coat the chicken evenly.

In a medium bowl, whisk the soy sauce, rice wine vinegar, ginger, orange juice, orange zest, and brown sugar. Add 1 teaspoon of cornstarch and whisk until it dissolves.

In a large non-stick pan, heat the vegetable oil over medium-high heat. Cook the chicken pieces until they are cooked through, turning once. Transfer the cooked chicken to a plate or cutting board.

In the same pan, cook the bell pepper until it softens, about two to three minutes. Add the orange sauce and bring it to a boil, stirring frequently. Let the sauce bubble and simmer until it thickens enough to coat the back of a spoon.

Add the chicken to the pan and stir to coat it in the sauce. Serve the orange chicken with cooked rice and garnish with sliced green onions.