Start by cutting the boneless chicken thighs into 1-inch slices. In a bowl, mix garlic, ginger, soy sauce, vinegar, chili sauce, salt, and pepper. Coat the chicken in this delicious marinade and let it sit for at least 20 minutes, or ideally overnight in the fridge for deeper flavor.

Heat oil in a deep pan over medium-high heat until shimmering but not smoking. Carefully add the marinated chicken pieces, frying them for about 5-8 minutes until they are golden brown and crispy. Drain them on paper towels.

While the chicken is frying, mix together the extra soy sauce, additional vinegar, and water to create a stir-fry sauce. In a separate bowl, combine cornstarch with water to create a slurry.

In a hot wok or a large skillet, add a little oil and sauté the finely diced ginger, garlic, and green chili for about a minute. Then, toss in the red onions and bell peppers, stir-frying them for 2-3 minutes until they are cooked but still crunchy.

Add the white parts of the spring onions, the prepared stir-fry sauce, and the cornstarch slurry to the vegetable mix in the wok. Cook until the sauce thickens slightly. Finally, add in the fried chicken pieces, tossing everything together gently until the chicken is evenly coated. Garnish with the green parts of the spring onions and sesame seeds before serving hot.