For the Beef:

• 8 oz flank, skirt, or sirloin steak, thinly sliced against the grain

For the Udon:

• 2 (7 oz) packs cooked or frozen udon noodles

For the Sauce:

• 1 tbsp vegetable or avocado oil
• ½ small onion, thinly sliced
• 3 garlic cloves, minced
• Optional: sliced scallions, sesame seeds for topping
• 2 tbsp low-sodium soy sauce
• 1 tbsp oyster sauce (or hoisin sauce for vegetarian version)
• 1 tsp sugar
• 1 tbsp cornstarch mixed with 3 tbsp water (slurry)
• 1 tsp freshly cracked black pepper (or more to taste)
• ½ tsp sesame oil
• Optional: 1 tbsp rice vinegar or Shaoxing wine