Cook the rice noodles according to package instructions. Drain and set aside.

In a large skillet or wok, heat the vegetable oil over medium-high heat. Add the sliced flank steak and cook for about 3-4 minutes until browned. Remove the beef from the skillet and set aside.

In the same skillet, add the minced garlic and ginger, cooking for about 30 seconds until fragrant.

In a small bowl, whisk together the soy sauce, brown sugar, rice vinegar, sesame oil, and red pepper flakes. Pour this sauce into the skillet and bring to a simmer.

Add the bell peppers and snap peas to the skillet, cooking for about 2-3 minutes until they are tender-crisp.

Return the cooked beef to the skillet and add the drained noodles. Toss everything together until well combined and heated through, about 2 minutes.

Garnish with chopped green onions and sesame seeds before serving.