Preheat the oven to 200°C (180°C fan/Gas Mark 6).
Peel the potatoes and cut into 1cm-thick chip shapes. Rinse under cold water, then dry thoroughly.
Toss the dried chips with 3 tbsp vegetable oil and a pinch of salt on a large baking tray. Spread in a single layer.
Roast for 30–40 minutes, flipping halfway, until golden brown and crispy (or air-fry at 190°C for 20–25 minutes, shaking occasionally).
Meanwhile, finely chop the white onion, red and green bell peppers. Mince the garlic and ginger. Slice the red chilli and chop the spring onions.
Heat 1 tbsp vegetable oil in a large frying pan or wok over medium-high heat. Add onion and bell peppers and stir-fry for 5–7 minutes until slightly softened.
Add garlic, ginger and red chilli to the pan and stir-fry for 1 minute until aromatic, taking care not to burn the garlic.
Add the roasted chips to the pan. Sprinkle over the salt, black pepper and Chinese five-spice powder. Toss well to coat.
Stir in most of the spring onions, reserving some for garnish. Serve immediately, garnished with the remaining spring onions.