Slice the beef into 1/2-inch thick strips across the grain for tenderness.

In a bowl, whisk together the soy sauce, white sugar, cornstarch, and ground ginger until the mixture is smooth and the sugar is dissolved.

Coat the beef slices thoroughly in the marinade, ensuring even coverage.

Heat 1 tablespoon of vegetable oil in a wok or large skillet over medium-high heat. Cook the beef strips in batches, stirring frequently until browned, about 3 minutes. Transfer to a bowl and set aside.

In the same wok, return the seared beef and add the red onion. Toss and cook for about 2 minutes until the onion begins to soften.

Stir in the green bell pepper and continue cooking for 2 minutes until it becomes vibrant and tender.

Add the tomato wedges to the wok and stir everything together to combine the flavors.

Serve the dish immediately, ideally with steamed rice.