Combine the ingredients for the marinade. Add chicken and marinate for 15 to 20 minutes.
In a separate bowl, mix together the sauce ingredients: orange juice, chicken stock, sugar, soy sauce, salt, and sesame oil. In a small to medium sized pot, heat up a few teaspoons oil and sauté minced garlic until fragrant, about 1 minute. Add apple cider vinegar, then the combined sauce ingredients. Simmer until liquid is reduced by three fourths, about 15 minutes. Stir in cornstarch and water mixture until sauce thickens, then season with salt to taste. Set sauce aside and keep warm.
Drip excess marinade off the chicken, and toss cubes in 1 cup of cornstarch. Shake off excess before frying.
Meanwhile, heat up the 3 cups oil in a wok. When oil just begins to smoke, add the first batch of chicken cubes and deep-fry until cooked through, about 4 to 5 minutes. Remove chicken with a slotted spoon and drain on paper towels. Repeat with the rest of the chicken.
Reheat orange sauce and add drained chicken cubes. Mix until well-coated. Plate and sprinkle sesame seeds on top.