Thinly slice your choice of flank, skirt, or sirloin steak against the grain, ensuring each piece is tender. Season lightly with salt and pepper, then optionally toss with a tablespoon of soy sauce and a cornstarch dusting for extra tenderness. Let this sit while you gather your other ingredients.

In a small bowl, whisk together 2 tablespoons of low-sodium soy sauce, 1 tablespoon of oyster sauce, 1 teaspoon of sugar, 1 teaspoon of freshly cracked black pepper, and ½ teaspoon of sesame oil. Then, prepare a cornstarch slurry by mixing 1 tablespoon of cornstarch with 3 tablespoons of water. Combine everything in the bowl and set it aside.

Heat 1 tablespoon of vegetable or avocado oil in a large skillet over medium-high heat until shimmering. Add the seasoned beef in a single layer and sear for about 2-3 minutes until browned and cooked through. Remove the beef from the pan and set it aside.

In the same skillet, add another splash of oil if needed, followed by the thinly sliced onion and minced garlic. Sauté for 1-2 minutes until the onion becomes translucent and the garlic is fragrant but not browned.

Add the cooked udon noodles into the skillet. Pour in the prepared sauce, and using tongs, toss everything together until the noodles are well-coated. Cook for another 2-3 minutes until heated through.

Return your seared beef to the skillet, gently folding it into the noodles and sauce mixture. Continue to stir until everything is well-combined and heated for another minute.