2 cups cooked rice (preferably sticky), for serving
Season chicken with salt and pepper. Heat oil in a large skillet over medium-high heat. Cook chicken, stirring occasionally, until opaque and golden brown in places, about 3 minutes. Add garlic and ginger, stir, and cook until fragrant, about 30 seconds. Add fish sauce, coconut milk, and 1/2 cup pineapple; bring to a boil. Stir, reduce heat to low, and partially cover. Simmer until chicken is cooked through, about 8 minutes. Divide chicken and sauce among serving bowls.
Stir together remaining pineapple, scallions, and chile in a bowl. Serve chicken with sticky rice and pineapple salsa.