Pat chicken dry and season both sides with salt and pepper.

Heat oil in a large skillet over medium-high heat. Add chicken and sear 3–4 minutes per side until golden. Transfer to a plate.

In the same skillet, lower heat to medium and add the sliced onion. Cook until soft and translucent, about 4 minutes, stirring to lift browned bits off the pan.

Add garlic and ginger for 30 seconds until fragrant.

Stir in soy sauce, brown sugar, and rice vinegar. Let the mixture bubble and thicken slightly. Add the pineapple chunks and red pepper flakes if using.

Nestle the seared chicken into the sauce, spooning some over the pieces. Reduce heat to low, cover, and simmer 8–10 minutes, or until chicken reaches 165°F and is tender.

Rinse rice under cold water until water runs clear. In a medium saucepan, combine rinsed rice, coconut milk, and water or broth with a pinch of salt.

Bring to a simmer, then lower heat to the lowest setting, cover, and cook for 15 minutes. Remove from heat and let steam covered for 10 minutes before fluffing with a fork.

Spoon the glossy pineapple sauce over the chicken, sprinkle sliced green onions and cilantro, and serve with a wedge of lime alongside the fluffy coconut rice.