Chicken Mee Goreng: Spicy, sweet-sour Singaporean noodles

Ingredients

• 100g potato, peeled, diced
• 225g fresh Hokkien noodles
• 2 stems choy sum
• 6 green onions, sliced on the diagonal
• 1 piece fresh hard bean curd, diced
• 2 tablespoons Sambal Goreng, plus extra for serving
• 1 tablespoon kecap manis
• 1 tablespoon oyster sauce
• ¼ cup water
• 2½ tablespoons vegetable oil, or more if needed
• ½ brown onion, cut into slivers
• 150g chicken thigh fillet, cut into bite-sized pieces (about 3cm)
• 1 egg
• ½ lime