Preheat the oven to 400°F.
Peel the potatoes and cut them into 1/2-inch-thick fries. Rinse under cold water, then pat dry thoroughly.
Toss the dried fries with 3 tablespoons of vegetable oil and a pinch of salt on a large baking sheet. Spread them in a single layer.
Roast for 30–40 minutes, flipping halfway through, until golden brown and crispy. If you’re using an air fryer, cook at 375°F for 20–25 minutes, shaking the basket occasionally.
Meanwhile, finely chop the white onion, red bell pepper, and green bell pepper. Mince the garlic and ginger. Slice the red chili pepper and chop the green onions.
Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the onion and bell peppers and stir-fry for 5–7 minutes until they start to soften.
Add the garlic, ginger, and red chili pepper to the pan and stir-fry for 1 minute until fragrant, taking care not to burn the garlic.
Add the roasted fries to the pan. Sprinkle with fine sea salt, freshly ground black pepper, and Chinese five-spice powder. Toss well to coat.
Stir in most of the chopped green onions, reserving a few for garnish.
Serve immediately, garnished with the remaining green onions.