Cut chicken into 1-inch cubes. Pat the pieces dry with paper towels to ensure better browning.
If using cornstarch for crispier chicken, toss the dried chicken pieces in 1 tablespoon of cornstarch until lightly coated.
Heat a large non-stick skillet or wok over medium-high heat. Add 1 tablespoon of neutral oil.
Once hot, add chicken pieces in a single layer (avoid overcrowding). Cook for 3-4 minutes per side until golden and cooked through to an internal temperature of 165°F.
In the same pan (or a separate saucepan if using air fryer method), combine orange marmalade and soy sauce. Heat over medium, stirring occasionally until bubbling and slightly thickened, about 2-3 minutes.
Return cooked chicken to the pan with the sauce (or pour sauce over air-fried chicken). Toss until each piece is thoroughly coated in the glossy orange sauce.
Allow to simmer for 1-2 additional minutes for the flavors to meld perfectly.
Garnish with optional sliced green onions and sesame seeds if desired. Serve hot over rice.