Bring a medium saucepan of water to a boil. Add the ramen noodles and cook until tender, about 2 minutes. Drain the noodles and set aside.

In a bowl, whisk together 1/3 cup soy sauce, 1 tablespoon brown sugar, 2 teaspoons sriracha (optional), 2 teaspoons minced garlic, and 1 teaspoon minced ginger. In a small cup, stir 1 tablespoon corn starch with 2 tablespoons water until smooth, then whisk the slurry into the sauce. Set the sauce aside.

Heat a large skillet over medium heat. Add 1 pound lean ground beef and cook, breaking it apart, until no longer pink, about 5–7 minutes. Drain any excess grease, transfer the beef to a bowl, and set aside.

Return the skillet to medium heat and add 1 tablespoon sesame oil. Add 1 large chopped onion, 1 chopped red bell pepper, 1/2 pound broccoli florets, and 1 cup shredded carrots. Cook, stirring occasionally, until the vegetables are tender-crisp, about 6–8 minutes.

Add the cooked ground beef and drained ramen noodles to the skillet with the vegetables and toss to combine.

Pour the prepared sauce over the noodle, beef, and vegetable mixture. Stir and cook over medium heat until the sauce comes to a simmer and thickens, about 1–2 minutes, coating everything evenly.

Remove from heat, garnish with sliced green onions and sesame seeds, and serve immediately.