Start by slicing the chicken into thin strips. Place them in a large resealable bag with cornstarch, seal, and shake until every piece is coated. This creates a light, crisp layer that holds up well when sauced.
Heat the vegetable oil in a skillet over medium-high heat. Add the coated chicken pieces and cook until golden brown and cooked through, about 4–5 minutes per side. Transfer to paper towels to drain excess oil.
In the same skillet, whisk together garlic, ginger puree, Sriracha, sesame oil, rice vinegar, brown sugar, and soy sauce. Bring to a gentle boil, then reduce the heat and simmer for 2–3 minutes until it thickens slightly.
Return the fried chicken to the skillet, add chopped green onions, and toss everything together until the sauce coats each piece. Cook for another 2 minutes so the flavors blend perfectly.