Season the chicken with salt and black pepper. Prepare all the other ingredients for stir-frying as you’ll need to move quickly once it gets going.
Heat the oil in a large wok or frying pan over a high heat. Stir-fry the chicken until half cooked through, then remove from the pan, leaving the oil behind.
Over a medium heat, soften the onion. Add the garlic and smashed ginger slices and cook for a minute. Then add the chilli and spring onion and stir through. Finally, in goes the tomato. Stir-fry everything for a minute more.
Return the chicken to the wok and add 175 ml (¾ cup) water. Season with oyster sauce, soy sauce and palm sugar: umami, salty, sweet.
Bubble until the chicken is cooked through and succulent and the liquid has reduced to a glossy sauce. Finally, stir through the kecap manis and taste for seasoning.