In a medium bowl, stir fresh orange juice, tomato sauce, orange juice concentrate, orange marmalade, brown sugar, soy sauce, chili garlic sauce, garlic, and ginger together until combined. Set aside.
Heat a large, heavy skillet over medium heat.
Add the avocado oil and carefully swirl around the pan.
Stir in the diced chicken breast, and cook through, stirring regularly. Chicken should reach a temperature of 165F.
Remove chicken to a plate and tent with aluminum foil to keep warm.
Add the sauce to the now-empty skillet.
Cook, stirring the entire time, until the sauce has reduced to about 1/2 cup. Reduce the heat if necessary.
In a small bowl, stir the cornstarch and water together.
Stir into the sauce and cook for about 1-2 minutes, or until slightly thickened.
Stir the cooked chicken back into the sauce and toss to coat in sauce.
Notes
For a more savory sauce, don't pack the brown sugar or reduce to taste.
For a spicier sauce, use more to taste. If you prefer even more heat, use red pepper flakes to taste.