Toast the desiccated coconut in a small pan over medium heat for 2-3 minutes, stirring occasionally, until light brown. Transfer to a bowl to cool.
Toast the cashew nuts in the same pan over medium heat for 2-3 minutes, stirring occasionally, until fragrant. Transfer to a bowl.
Heat the oil in a wok over medium heat. Add the onion, garlic, chilli peppers, and both bell pepper pieces (red and green). Cook for 2 minutes, stirring frequently, then remove and set aside.
Increase the heat to high. Add the chicken pieces in two batches, cooking each batch for 3-4 minutes, stirring occasionally, until light brown and cooked through (internal temperature 74°C / 165°F).
Return the cooked onion and pepper mixture to the wok. Add the oyster sauce, fish sauce, sugar, and pineapple. Cook for 2 minutes over medium-high heat, stirring gently. Fold in the toasted cashew nuts.
Transfer the chicken mixture to a serving platter. Sprinkle with the toasted coconut and spring onions. Serve immediately with rice.