Prepare the Potatoes: Rinse the julienned potatoes in cold water and drain well. This helps to remove excess starch, ensuring they stay crisp when stir-fried.

Warm the Oil: In a spacious skillet or wok, heat the vegetable oil over medium-high heat.

Sauté Garlic and Onions: Add the minced garlic and sliced onion to the hot oil. Stir-fry for 1-2 minutes until fragrant and the onions are slightly softened.

Cook the Potatoes: Add the julienned potatoes to the skillet and stir-fry for about 5-7 minutes, stirring frequently, until the potatoes start to soften but retain a slight crispness.

Add Remaining Ingredients: Add the red bell pepper (if using), soy sauce, vinegar, salt, black pepper, and chili flakes. Continue to stir-fry for an additional 2-3 minutes until all the flavors are well combined and the potatoes are cooked to your liking.

Finish with Green Onions: Add the chopped green onions, stir well, and cook for another minute. Taste and adjust seasoning if needed.

Serve: Transfer the stir-fried potatoes to a serving dish. Serve hot as a side dish to complement your favorite main course.