In a large skillet heat oil, over medium high heat. Add ground chicken and cook, crumbling with a wooden spoon. Stir in the onion and cook on medium heat 3-5 minutes, until translucent. Add the grated garlic and ginger and cook 30-40 seconds, or until fragrant. Stir in the hoisin sauce, soy sauce, rice wine vinegar, chili sauce, water chestnuts, pineapple (if using), salt, and black pepper; cook for 3 minutes.