In a bowl, mix the diced chicken breast with cornstarch until well coated.
In a large skillet or wok, heat a tablespoon of oil over medium-high heat. Add the chicken pieces to the pan in a single layer and cook until golden brown and cooked through, about 5-7 minutes. Remove the chicken from the pan and set aside.
In the same skillet, pour in the orange juice and soy sauce. Stir well and bring to a gentle simmer.
Return the cooked chicken to the skillet, stirring to coat it evenly with the orange sauce. Let it cook together for an additional 2-3 minutes, allowing the sauce to slightly thicken.
Once the sauce is glossy and has thickened to your liking, remove from heat and serve immediately.
Notes
Serve over steamed rice or quinoa, garnished with green onions and sesame seeds.