Start by blitzing ginger, garlic, and onion in a food processor to create a smooth paste. Reserve 2 tablespoons of this aromatic mix for later.

Cut the boneless chicken into 1-inch pieces and marinade with ginger-garlic-onion paste, soy sauce, chili powder, black pepper, and a splash of water for at least 1 hour in refrigerator.

Finely chop the sweet red bell pepper and set it aside for later.

In a medium bowl, whisk together tomato paste, oyster sauce, sugar, dark soy sauce, regular soy sauce, rice vinegar, chili powder, and water to make the sauce.

Mix cornstarch with cold water until smooth in a small bowl to prepare the cornstarch slurry.

Heat oil in a deep pan to 350°F (177°C), coat marinated chicken with cornstarch mixture, and fry in small batches until golden brown.

In a separate pan, heat oil and stir-fry the reserved ginger-garlic-onion mix until golden, then add the chopped bell peppers and sauté until softened.

Add the prepared sauce mixture to the pan, combine well, and cook for about 2-3 minutes until thickened. Toss in fried chicken to coat with sauce.

Serve hot, garnished with cilantro if desired, alongside steamed rice or Hakka noodles.