Marinate the beef with soy sauce and vinegar for 10 minutes.
Heat vegetable oil in a large skillet over medium-high heat.
Add minced garlic and sauté until fragrant.
Stir-fry the marinated beef until browned, about 5 minutes.
Add sliced onions and cook until translucent.
Mix in the sliced tomatoes and cook for an additional 3 minutes.
Season with salt and pepper to taste.
Add pre-cooked French fries and toss to combine.
Garnish with fresh cilantro before serving.
Serve hot, ideally over rice or with additional fries on the side.