Begin by preparing all your ingredients to make your cooking process smooth. Thinly slice the beef sirloin into strips and set aside. Mince a few cloves of garlic and chop one onion into small pieces. Dice a vibrant red bell pepper and gather your cooked noodles.

In a large skillet or wok, heat 2 tablespoons of vegetable oil over medium-high heat until the oil shimmers.

Add the sliced beef sirloin to the hot skillet in a single layer. Sear the beef for 3-4 minutes until it turns brown and develops a nice crust.

In the same skillet, add the minced garlic and chopped onion. Sauté for 1-2 minutes until fragrant and the onions begin to soften.

Toss in the diced red bell pepper and sauté for an additional 2-3 minutes until tender-crisp.

In a separate bowl, whisk together 3 tablespoons of soy sauce, 1 tablespoon of brown sugar, 2 tablespoons of gochujang, 1 tablespoon of sesame oil, and 1 tablespoon of rice vinegar until smooth.

Pour the prepared sauce into the skillet with the sautéed vegetables, stirring well to combine. Let the mixture simmer for about 1-2 minutes.

Return the browned beef to the skillet, tossing everything to ensure it's well-coated in the flavorful sauce.

Add your cooked noodles directly to the skillet, gently tossing everything together for about 2-3 minutes.

Finally, sprinkle sesame seeds and sliced green onions over the top of your plated Korean Gochujang Beef Noodles, serve hot.