In a mixing bowl, combine the cornstarch, salt, and pepper. Toss the chicken thighs in the mixture until evenly coated.

Heat vegetable oil in a large skillet over medium-high heat. Add the coated chicken thighs and cook until golden brown and cooked through, about 5-7 minutes per side. Remove the chicken from the skillet and set aside.

In the same skillet, add garlic and ginger. Cook for 1 minute until fragrant. Add orange zest, orange juice, soy sauce, brown sugar, rice vinegar, and sesame oil. Stir to combine and bring to a simmer. Cook for 2-3 minutes until the sauce thickens slightly.

Return the cooked chicken to the skillet and toss to coat in the sauce. Cook for an additional 2-3 minutes until the chicken is heated through. Serve the orange chicken over rice or noodles, garnished with sliced green onions and orange slices.