Start by preparing all of your ingredients. Slice the beef into thin strips, ensuring uniformity for even cooking.

Wash and cut the bell pepper into thin slices, and mince the garlic and ginger. Slice the red chilies, adjusting the amount based on your heat preference.

In a mixing bowl, combine the beef strips with soy sauce and cornstarch. Make sure each strip is well-coated.

Allow the beef to marinate for about 30 minutes.

In a large pan or wok, heat vegetable oil over medium heat until it shimmers.

Carefully fry the marinated beef strips in batches until golden brown and crispy, approximately 4-5 minutes.

Set the beef aside on paper towels to drain any excess oil.

In the same pan, add the minced garlic, ginger, and sliced red chilies. Sauté for about 2-3 minutes until fragrant.

Add the sliced bell pepper to the pan and sauté for another 2-3 minutes.

Sprinkle sugar over the sautéed vegetables and pour in the vinegar. Season with salt, letting the mixture simmer for about a minute.

Return the crispy beef to the pan and toss everything to ensure the beef is well-coated with the sauce and mixed with the veggies. Allow it to cook for an additional minute before serving.