Heat oil, then sauté beef, onion, broccoli, and bell pepper until tender.
Stir in garlic and cook for 1 minute until fragrant.
Whisk soy sauce, vinegar, water, sugar, ginger, and cornstarch slurry in a bowl.
Add sauce to pan; simmer until thickened and glossy.
Toss in noodles; mix until evenly coated.
Season with salt and pepper, garnish with green onions, and serve warm.
