Pound the chillies and garlic to a coarse paste. Use a mortar and pestle for this or chop the chillies and bruise the garlic with the back of a knife. Chop the chicken into bite-sized pieces.
Heat the oil in a large wide pan or wok. Add the pounded chillies and garlic and cook until fragrant - about 2 mins.
Add the chicken pieces to the pan. Keeping the heat on high, disperse the chicken pieces in the pan so they are in an even layer without too many overlaps. Don’t be tempted to move them around. Let the pieces colour on the first side before you stir and cook the other side.Note: do this in batches if you're cooking a big batch and/or using a small pan. Test a piece to make sure the chicken is cooked through. Add in the oyster sauce, dark soy and soy. Cook for a further 5 mins turning the chicken in the sauce.
Scrape up all the sticky bits from the bottom of the pan. All this is flavour we want. If it appears too dry, add a bit of water and cook for a few mins. If it’s too wet, turn the heat up and let some of the liquid evaporate. Taste and adjust seasoning.
Stir in the basil leaves and wilt for no more than a minute. Best served with rice and a side salad or vegetable.